I found Photoshop's UI scaling doesn't work in Windows 11, but Illustator and Indesign work very well. Comparing the setting interface below, I really think the Illustator one is much more straightforward and easier.
There is a fundamental difference between Photoshop and Illustrator/InDesign that few people understand the implications of:
Ai/Id are vector applications that will always, under all circumstances, render content at full screen resolution. So when they scale up for a high resolution screen, they can just scale everything, interface, image, the whole thing.
Photoshop, as a pixel-based raster editor, is a special case. It needs to scale up the interface, but cannot scale up the image. The two must be treated separately. That's a very different proposition that requires special coding, special support from the operating system etc. If that wasn't so, the high resolution display would be wasted. You could just as well use an old standard HD screen.
The way this works is that Photoshop atomatically picks up the scaling factor you set in Windows, and uses this for the interface (but not the image). This only works for Windows past a certain version (can't recall which, somewhere around 2019/2020)
Leave Preferences > UI scaling on Auto, don't touch it. Just set it in Windows.
That's a lot of bold italic, sorry about that, but these are crucial things to be aware of.
Gotcha! I don't know programming, and I thought interface and function were different things that could be treated separately. Thank you for your reply.