Hello, I really want to play this game but trying to compensate for the 21:9 issues (mouse location doesn't coincide with the desired action, doesn't track) is quite irritating. There is a Steam mod, however, I can not find one for the GOG version. Any help? Thanks.

Where is this Steam mod that you're referring to? All I can find on Steam is mention of a file edit mod which I believe is likely just an ini file edit which fixes the HUD but does NOT fix the mouse issue.

As far as I can tell from my research there has never been a fix for the mouse issue.