F12 only. That key does not usually work with rpg maker games or indie games. You can try key mapping it to a different key to see if it works.

As for print screen, that will not work. Unless you first make a copy on paint, save it as a jpeg less then 5mb, then save as a artwork piece. It is a longer method to do though. I think i wrote a guide about it several years ago. Ill try to find it for you.

Any images outside of Steam use Artwork in your profile looks exactly the same results it will be viewed online.

It's possible using URL manipulation, but it's been so long since I last did it that I can't remember the steps.

When F12 doesn't work, it's usually because the overlay (shift+tab) is disabled or not working. This article might help you get it working:

https://psteamhelp.yuanyoumao.com/en/faqs/view/3978-072C-18DF-FBF9

on zawg and schlawg

引用自 stemy：

Is it possible to upload the screenshot taken with PrintScreen on Steam or i works only with F12.

Yes, with a free program called SteaScree you can upload anything as screenshot.