Whenever I try to play from the launcher, it has the MB2 startup loading screen, but when I actually get to the main menu, its the Base JA UI lol. I uninstalled and reinstalled, but still have the same issue.
Temporarily remove any third party mods / pk3s from base and MBII
Run a repair from the launcher's settings
Enable logging in launcher settings, restart the launcher, start the game, and then post the log here (if you use your real name as your computer account's username, you'll want to do a find/replace to anonymize it)
Issue was the game not being able to properly load mod DLLs:
And that was because of a bad antivirus program throwing false positives and blocking them from being read out of MBII.pk3 at startup. After uninstall everything worked fine with the built-in Windows Defender.