you might have a partial solution here:
AppDeployToolkitMain.cs could not be opened - The Toolkit / General Discussion - PSAppDeployToolkit Community
If you get it working, please report back .
There is also another solution here but it’s not official (aka Merged-in)
precompiled cs as wdac audit enable breaks ADT by Numidian · Pull Request #819 · PSAppDeployToolkit/PSAppDeployToolkit (github.com)
It involves replacing AppDeployToolkitMain.cs with AppDeployToolkitMain.dll !