Appreciate the response. Problem with a separate Steam game is that it's not running under the actual Far Cry game, so game time isn't counted and screenshots aren't saved to that community hub. Basically we need the Steam overlay to work running this mod while Steam thinks we are playing the og Far Cry.
Got it, will investigate it and then tell the results. UPD: Solved. Answer is here: https://farcry1.itch.io/far-cry-advanced-version/devlog/924916/how-to-play-fcav-via-steam-with-overlay-far-cry-fixes