The game crashes.

The game crashes a little to much. When I started to playing the game it was during 1.15.2, but when I tried to go back to 1.12.2 (I have played this version before but, on xbox) however, once I try to go back (while using forge) it tells me that the game has crashed WITHOUT telling me the issue and how to fix the issues. Another thing that I don't understand is why doesn't it have a guide to show how it works? (I searched and can't find it) I would've excepted it to show you how to go back to different version of minecraft, BUT NOPE. nothing. I have to look it up. that to me is considered a little unprofessional. nobody's like to spend their time on looking it up on youtube when you could just add it to the game. A the end of writing I rate the game a 3 1/2 stars, it's missing a lot of things could just make the game better.