Use some overlay like MSI Afterburner and set that on F12 or wherever you like, then you can even disable Steam's and use that universally for everything. Alternatively Windows key + print screen will save a picture automatically (the screen will dim for a moment to let you know it worked) rather than have to paste it in like with just print screen and it works whether you're in a game or not. All this can vary if the game does something weird with rendering as usual, you might get your desktop screenshot even though the game's over it or whatever, but commonly it all works.