Hello,
in my case, it was MSVC++ missing runtime.
Go to : C:\Program Files\Microsoft Azure AD Sync\Bin\
Run : miiserver.exe
If you have an error message with missing MSVCRxxxx.dll then you have to download an install VC++ 12 from here :
https://learn.microsoft.com/fr-fr/cpp/windows/latest-supported-vc-redist?view=msvc-170
That's surprising that VC++ 14 is not supported.