Just to clarify, I’m one of the Moderators on The Forge Discord, and what I ran through in my last post was indeed technical help.
Checking world size: World Size Check
Clean out things you don’t need into Compendiums. Slim the world down. If the world won’t migrate, it’s an issue with the world in all likelihood. Watch the Dev Console (Press F12) for Migration progress, and especially for Errors (Red Text).
The Module part is to help you going forward, as you can clean out things that would cause you other issues with FoundryVTT Performance: Trouble with Modules