Well, about you mentioning "decompile" one time, I will decompile your build, get the correct Unity version that was used for Baldi 1.4.3, open the project with the Unity version, re-implement the scripts, fix issues, change the Warning screen a bit, and these changes:
Character Controller component changed back to Rigidbody component
Change lighting theme from the project having Lightweight Render Pipeline to the project having the "School" scene having Cubemap lighting
Position changed for the desk to the old position of itself from the original 1.2.2 build (2017.3.1f1 build) of the desks in the you-know-what faculty room
Remove textures that are unnecessary
Remove TextMeshPro
...and other things I forgot or don't know how to mention.
And that's it!
EDIT: I actually looked in the code while working on Nostalgia, I now know it's your attempt of fixing the graphics. However, the settings for the graphics is different than we're supposed to expect, but it's not working because there are material issues, wrong graphics options, and there's not a Cubemap.