Perhaps try opening the epic launcher and verifying your engine install, maybe something got corrupted with it’s files.
UE4 (at least 4.27) does not have a UE4.exe file. These are the ue4 executable files in the Binaries\Win64 folder
Do you have the needed MSVC version and Windows SDK installed for the older of Unreal? This is usually the culprit if old project don’t compile nicely.