I just tried the trial version of Mask AI to try to remove a person from a relatively tricky background, as a test. It didn’t do very well at all, especially with the hair. Very disappointing! I will not be buying it.

I had exactly the same issue. I contacted Luminar (Skylum) tech support. First thing they said was to use “Export “ instead of “Edit In “ to get the photo into from Lightroom into Luminar. This worked most of the time. The next thing they suggested was to reinstall the Luminar plug in component. I did that as well and also seemed to help. I eventually got it working consistently but it took a while.
In my case I think the problem was a problem in Windows 10 following one of their updates!

I had the same issue you’re describing on a Windows 10 PC. I could not open the program either as a free standing program nor as a Lightroom Plugin. I decided to do an uninstall and reinstall. However, when I went to uninstall the program I noticed a checkbox to repair the program instead. So I tried the repair process. That did the trick for me. It now works fine as a plug-in and as a freestanding program.

Do a search on YouTube for videos on using a DSLR as a webcam. There are a number of them that will show you how to do it without the need to purchase a video capture card. See link below.
https://youtu.be/JXhYgybNz0I

In addition to the lenses you mention, take a fast prime, 35mm or wider or even a 50mm, f1.8 minimum. You will need it in some of the Churches and shrines where you won’t be able to use a tripod or flash. I was there a couple of years ago. It was one of my favorite places to visit and hope to get back.
You will love it, it’s very special, no matter what your religious beliefs!

Thank you for his service and condolences for your loss.

Check the Buy/Sell board on Fredmiranda.com. There are a number of A7R3’s for sale there.
Good luck