There's a shortcut, I think you can set it within the Steam settings (not within the FM options). Mine is set to F12, not sure if that's the default. The screenshots are then saved into your Steam profile folder, so they'll be in C:\Program Files\Steam\userdata\00000000\000\remote\000000\screenshots. The numbers where I put 0s appear pretty random, I think they're somehow related to steam profile IDs and stuff like that. Just look through your Steam settings and you'll find the option.
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