If you play the mod on Windows Mac or Linux, download this file: https://www.mediafire.com/file/n2n10b5uzw6w09a/Assembly-CSharp.dll/file to Mod Folder > Baldi Basics Ultra Decompile_Data > Managed and replace the file to the one you downloaded. Letting you know this because I forgot to add a major code for "V3 Update" and it kinda messed everything up. Please do this if you want to play the mod with no issues. If you are on android, unfortunately you're going to deal with the issues for now until I figure out a fix for android.
Viewing post in Baldi's Basics The Ultra Decompile comments
And if anyone asks why downloading this, it's a thing that I'm testing for school updates without downloading the game. Not doing it all in one because it's going to take a while to do it. So yeah, you do not need to update the game for the new schoolhouse coming up because it'll take a while to be finished.