Looks like an issue between Mekanism and Forge
You can try to downgrade Forge to 1.15.2 - 31.2.0
or test an older version of Mekanism
Not trying to be rude at all. But if you trying to figure how to create modpacks its best to learn how to read crash logs. Again not trying to be rude but just saying my though of advice.
Pls don't reply to treads if you can't give any solution. In this case CookingForBlockheads hides the issue - even a person who can understand crash-reports would in this case not see the issue ...