.bat file will not work with steam.
You can try to add manually farcry.exe from OpenFC in steam as separated game. Also, about screenshots, they saves into: "YourFarCryFolder/FCAV_Files/Screenshots", but yeah, that will not shown in steam. Okay, if still nothing will help, we will investigate this thing and will try to make special guide a bit later.
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
