I gave my last smart phone, an iPhone back to the company when I retired in 2014. I may have accidentally dropped it on the ground and stomped on it. I hated that thing. I had Android based phones prior to that last one. Anyway, for the past 7yrs I have had an ATT 3G dumb phone, but, ATT 3G service is ending next year. Finally accepted the inevitable and bought an iPhone12 since my wife has an iPhoneX and can give me tips. One problem. There are so many apps that I get a headache just looking through them. I would like some suggestions as far as the ones you find most useful for photography, such as remote camera control of my Canons, etc. I don't use social media so those are of no interest. Wait, I lie! I opened a Facebook page about 10yr ago for a class reunion but I haven't visited it in probably 9yrs. I don't even remember the password to log on.
I am actually starting to enjoy this new phone. Maybe you can teach an old dog new tricks. Any suggestions would be appreciated.

It seems to me that every day there is a unique, different, and obscure newfangled way of rating cameras as to sensor performance and a long list of ultra-minuscule microscopic standards that most probably would not to the average photograher- even advanced amateur and professionals. This ISO Performace has some relevance but is not, in my opinion, the singular determining factor in invest in a camera system.

Here's a link to an explanation of ISO performance.

https://vasphotography.wordpress.com/tag/iso-performance/

It kind of a gauge of signal to noise kinda thing. It is a measurement of noise at given ISO sensitivity settings- even low numbers like ISO 100 or 200. So a camera with a better rating will show less noise at high settings like 1000, 1600, 3200, etc.

This rating has nothing to do with the camera's maximum ISO setting in and of itself. It gauges performance at all the ISO settings that the camera offers.

The attribute factors in of you are printing or exhibit your work at great degrees of enlargement, especially if you are in many "black cat in a coal mine at midnight: situations and especially if you need to have high ISO settings, smaller apertures for depth of field, and faster shutter speeds to stop motion.

Depending on the kinds of work you are doing, comparing camera "A" to camera "B"- I would suggest there are many other factors to consider including ergonomic handling, format, lens and accessory selection, weight, portability, general build and quality, SLR or Mirrorless, and more- not to mention price and budget considerations!

Decades ago, in the film era, low light shooting involved high-speed coarse-grained film pushed processed in dynamite-like developers. This would yield excessive gran and oftentimes lack of shadow detail but a story-telling image was to be had. Nowadays in digital photography, even a high ISO setting- and even on some of the order mode cameras, the NOISE is not all that terrible. I have made mural-size display prints shot with an old D-300 and D-700 at ISO 800 and 1600 that were surprisingly "grainless"!

Simply works backward from the work you intend doig, the exhibition size, the light levels you may find yourself in, the need for high IOS settings, fast shutter speeds and small apertures and asses YOUR requiremets on that basis. If you really need that extra ISO performance- by all means, consider it. The ultimate test is in the results. Before investing in a system I want to get a thorough demonstration. Written specifications and claims are fine bit I wanna SEE the difference!

As BebuLamar noted those are DXOMark ratings. Here's what they say about those numbers:

"When shooting sports or action events, the photographer’s primary objective is to freeze motion, giving priority to short exposure times. To compensate for the lack of exposure, photographers have to increase the ISO setting, which results in a decreased signal-to-noise ratio (SNR). How far can ISO be increased while maintaining decent image quality? The DxOMark low-light ISO metric will give you this information.

The SNR indicates how much noise is present in an image compared to the actual image information (signal). The higher the SNR value, the better the image quality, as detail is not drowned out by noise. The SNR is given in dB, which is a logarithmic scale: an increase of 6 dB corresponds to doubling the SNR, which in turn equates to half the noise for the same signal. A SNR value of 30dB means excellent image quality. We have therefore defined low-light ISO as the highest ISO setting for a camera that allows it to achieve a SNR of 30dB while keeping a good dynamic range of 9 EVs and a color depth of 18bits. A difference in low-light ISO of 25% equals 1/3 EV and is only slightly noticeable. Low-light ISO is an open scale." https://www.dxomark.com/dxomark-camera-sensor-testing-protocol-and-scores/

That still leaves a lot of questions about their methodology but, fairly assuming they're consistent in what they do, you can at least use those numbers as side by side comparison values for their tests. In other words DXO assigns a higher value to a camera with better low-light performance on their tests is as much as you can take from them.

Do as Paul suggested and look at real samples from a reviewer like DPreview.