You can turn on 'Save an external copy of my screenshots' in Steam→Settings→In Game. This will save an uncompressed version in a custom folder (/Users//Documents by default).
You can also use Windows' built-in image tool (accessed using Win+Shift+S), or simply use PrtScr (or preferably Win + Prt Scn, as it will save the PNG right in your /Pictures/Screenshots folder and you don't have to paste the image first).
But instead of taking screenshots with Steam or Windows, I suggest using Nvidia overlay's Photo Mode (hotkey Alt+F2). You can double the screenshot's resolution (so you'll end up with an uncompressed screenshot 4 times the size of the resolution you're playing at), which usually works very well, and use custom filters to completely change the look and feel. This used to be Ansel (which was way better but replaced because reasons (i.e. enshittification)).
AMD Adrenalin has a similar option.
