In your first video, the error from halfway point to end of video is saying the enum is trying to use an unsupported type, that is because of a typo you made. Your code shows the enum as:
UENUM(BlueprintType)
enum class EFactionType : unit8
but it should be:
UENUM(BlueprintType)
enum class EFactionType : uint8
where you accidentally spelt uint8 as unit8.
Other errors you see can be caused by the first initial errors so ignore other errors and focus on the first errors that show up. The “OtherCompilationError(5)” and “-waitmutex” errors are just related to UE4 failing to compile due to your code errors so you can ignore those.
Use build instead of rebuild. If you want to build cleanly, especially after removing files, make sure to choose ‘Clean’ so that it cleans up intermediate files and then choose ‘Build’; you should find it then won’t be attempting to still use files you have removed from source.
Deleting all source files won’t work as UE4 can’t build without the specific base project files which are needed needed. Until you clean the build, you will likely still have intermediate files trying to reference files you have deleted as well. Those errors after deleting the ‘Source’ folder in your second video are due to having zero project source (as you deleted the base source files created by UE4 for the project which it needs for knowing how to setup your project and specific UE4 data).
Other errors:
In CharacterAI.cpp the OnSeePawn function has:
if (NeuralFactions.Contains(Player->GetFaction())
where you have a typo of NeuralFactions instead of NeutralFactions.
In Header1.h, at the start of the class declaration you have:
GENERATET_BODY() which should be GENERATED_BODY().