As already said above, your DX lenses on FX body will probably work (or may not- need to be checked), but that seems as wasting camera "optical resources".
You may continue to work with your D7200 or sell it together with belonging DX lenses.
Z5 is great camera (I own it). This is the lowest priced FX model on the market and the best in class.
You will need new lenses of course. You may skip kit lens, or you may decide to have it. Z lenses are generally superb. So far there are quite some released to choose from.
My recomendation is 24-200 Z f4-6.3. Amazing lens. Will cover your landscapes and every day fully.
Great fun with mirrorles cameras is using old manual focus lenses. You need "dumb" adapter but for Nikon F mount preAi and Ai original from Nikon FTZ will suite Nikon F AF-s and g lenses as well old manual ones.

Yes!
Four yeses!

There is yet one. Because of missing mirror, bodies are generally smaller.

And yet, Inspirion vs Latitude?
Latitude series is designed for bussiness application. Usually better and stronger case, stronger battery user replacable, screen quality, additional equipment like ports interfaces... Before Latitudes had "docking interface" at the bottom of the device. Today, newest Latitudes doesn't have that port anymore because USB C/Thunderbolt is replacement for special docking port.
Regarding CPU/RAM/Graph/Storage, Inspirion as well Latitude are build in so many configurations, so customer can choose from. According to that price vary a lot.

Wau! 5 pages of help.
Whenever one wish to buy a computer the main question is "what for?"
In you case seems it is Lightroom and Paintshop.
Here is what Adobe says for their LR requirements:
https://helpx.adobe.com/lightroom-classic/system-requirements.html#:~:text=Minimum%3A%20Recommended%3A%20Processor%3A%20Intel%C2%AE%20or%20AMD%20processor%20with,1920%20x%201080%20display%20or%20greater%3A%20Graphics%20card

"Minimum" column at link above is OK in most hoby cases. If you are pro and going to edit huge size files, and lot of them, probably not even "Recommended" column will satisfy.
Great help will be your expereance with your previous device while it was working. Analyze what CPU, clock cpeed, RAM and graphical was there and were you satisfied with. What operation do you remember it was strugling with?
i3 can be better choice then i7. I3 is much cheaper. Here is clock more important then number of cores.
And yet, if you want to safe money, why go with LR and PS? There are great alternatives: Darktable and GIMP. Opensource both are free and slightly less demmanding. Well, less demmanding in start but when you come to big files and mass exports or rendering more power and memory is essential too.
When you have your answers, then you know what you are looking for and what you can get for your budget.

5 minutes difference in time may produce great difference in light character. I observe both photos bit more and found that big difference in light happened indeed.
Compare the pine trees under the rock arch. At one photo pines are illuminated by the sun heavy. At other photo pines are almost completely shadowed. (Probably clouds on sky ) That may produce white balance difference in start point.
Everything else what is mentioned here regarding AI in phone is true. Designers of phone, made AI to produce attractive photos. Usually warmer and saturated look is more atractive. Raising dinamic range is another trick.

Look at the sky. Nikon see clear blue sky while phone made sky gray. So obviously AI isn't that perfect yet.
The main catch is that we need to know our camera better and make our effort to get photo better then silly phone did.

Confusing element lay in overlaping functions the two (exposure,contrast,color,curve.....)
Simplest explanation:
- RAW editors are used to finish the process started in camera, in order to get final usable photo format of single file.
- PHOTO editors are used to manipulate any photo format (jpg,png,tiff....) and make final design, like front page cover e.g. (You may combine multiply photos, titles, effects, or you may use that tool just to stick panorama, or focus staking photo serie, or night scape serie. Nothing of this is possible in raw editor). PS alsocontain a lot of tools specific to print technology,in order to prepare final design to different printing techincs and maximize color/brightness/contrast accuracy on paper.

So, PS and similar is more design tool, while LR and similar is photo developing tool.

Confirming everything what is said and warm recommendation. Besides, it works on Win/Osx/Linux.
Next step from that or in conjunction with would be Darktable. Also opensource, probably best next to Lightroom. Darktable is intended to edit and convert RAW files from camera to jpg, png, tiff... Also works on Win/Osx/Linux.
Both tools are quite serious. You need follow manual from basic to get there.

However, since declared as "newbie" I can recommend google drive/photo cloud. There is available google editing option online inside the browser. You can play with your jpgs as much you like learning basic editing functions.

In fact, I have found that all mirrorless brands introduced one quite important difference in compare to SLR/DSLR design. It is the way how lens aperture behaves in one or other case.
With SLR/DSLR lens is always full open. It is clossing to preset value in moment of triggering. Mirror goes up, aperturer closing to preset valu, I that moment we see dark anyway. This is important because that way maximum light is passed to optical viewfinder how photographer can better see and better focus if doing it manually. But also this way more light is passed to AF sensors too.
(I beleive that fast lenses are invented because of this at the first place)
Suddenly with mirrorless designers desided to close aperture proportionally as it is set by camera or photoghrapher. Interestingly, Sony closing aperture all the way fully closed, Nikon Z closing up to 5.6,don't know what Canon do. Then they do short mimic openning aperture shortly doing measurements and AF. If flash is used aperture is probably closed accordingly. Those are the reasons while we don't see anything in low light condition. Then they left us option to turn "real view" off, electrically amplifying signal for better see.
Using slow lenses in low light doesn't help either(but that is not news) just saying how problem becomes greater.

Bravooo! to donor.
Congrat to receipient.
D700 has one great option:may mount and work with all Nikon lenses SLR lenses ever produced. preAi,Ai,Ais which is big pool of amazing lenses if owner willing to experiment with manual focus lenses.
Happy hooting!

Also there where GOST russian nomenklature for the same purpose. About 90% of ASA value was contained in equivalent GOST value.
However, DIN norm was more in everyday use for us in Europe.

I don't know when "oldness" starts counting from, but very curious why 64Gb is most important to you?
Since I am not that young either, I am not quite sure when one playing with PC at home may need that huge amount of RAM?

Price matter.
Must be PC.
Light editing + storage + occasional printing.

Now we go:
RAM 8Gb will suite (DDR4+)
CPU - you can go even with i5 (not fully familiar with Ryzen but AMD should be even better). Good choice will be latest generation 9,10,11 (Intel). Better CPU will help but not that important for amateur use.
Graphic card, integrated is enough.
SSD disk is MUST today (could be SATA or better PCIe M2) additional non-SSD SATA drive for local storage.

OS: Win10 or 11 but also Linux (OpenSuse or Ubuntu)
RAW photo editor (free Lightroom replacement): Darktable (it works on Win, Linux and Mac)
Photo editor (free Photoshop replacement): GIMP (it works on Win, Linux and Mac)

I am working for decades on all 3 platforms with software above. Least used is windows. Until end of 2020. I was using MacBookAir 11" with i5 4Gb RAM on 125Gb SSD from 2014. I felt it bit getting slow when exporting RAW file to jpg as well the newest software upgrades needed more powerful CPU. Last year this was replaced with 13" Air with M1. No need to say how M1 is good and fast. Even Darktable is not compiled for M1 platform.
My weakest platform is i5 7600/ 16GbRam, integrated graphic, OpenSuse 15.3 + virtual Win10 on top of that. Using both. No flaws.
Editing RAW will need faster CPU during editing itself (time needed to render applied command) as well as exporting RAW to JPG. If those times are not drastically long, for non-professional use may be satisfied with slightly slower CPU.

In fact, it exist long time already. We don't need software at the first place It is only a math.
Photography we are used to is still analog presentation of light, pixels, dots.
More pixels, more colors, more deep...... more anything.... we are getting sharper, more contrast, more dinamics....

There is different way of presentation called vector presentation. There are no size limitation in order to present vectorised perfect sharp, perfect colored, graphon.
When we able to present photo based on different data then light itself, we will able to make blinds see. We will be able to see in the dark, in the past, in the future without any lens.

There are known limitation with "silent shutter", one of them is flash sync and control.
While control (TTL) will be hardly possible, would be possible to use flash in pure manual mode at lower shutter speed then sync speed designed for that camera.

I would also recommend to read camera manual.

I am completely disagree.
First of all shooting manually means exactly that: photographer choose parameters in order to get final result. Having light meter in camera is great. There is no other way in setting correct exposure then using measurements. Guessing is not very welcome way.

I think that your question is not correct. Camera is tool. It has built in options.
For me better question would be if camera owner knows and understand all camera possibilities and power as well weakness.

It is not strange that many people don't understand 90% of their camera functions and settings. That is why many cameras have "Auto" , "Inteligent Auto" or similar set point, and that will help people to take beautiful photos , almost as good as those taken by phone.