hi @Cleverlike_Studios
Your error log contains
Guid format shader working directory is -4 characters bigger than the processId version (C:/Users/yourName/AppData/Local/UnrealEditorFortnite/Intermediate/Shaders/WorkingDirectory/30488/).
This shows the corrupted shader area which is NOT cleared by verifying your UEFN installation.
There are lots of leftover files from the earlier UEFN versions.
This was solved in the post
31.20 [Solved] UEFN Fix Validation Error pop up wont “Run” - General / Issues and Bug Reporting - Epic Developer Community Forums (unrealengine.com)
This clears the areas programmatically