Hey @Shady1, thank you for helping me.
I forgot to mention that the 3 non-standard files were added the last time it crashed and I tried the windowed mode (it runs smooth in windowed mode). No idea why I did not remove them before I started the diagnosis, sry.
In this specific case they did not change the behaviour anyway.
1) Ultrathing v0.29 is only mod installed now and tabbing out of the game and clicking on it causes it to die.
It does not lag, crash or freeze ingame. The problem does only occur after tabbing out. It works in windowed mode without any problem.
2) Using the Steam Version somehow resolved the problem without the mod installed (so without UltraThing installed).
Additionally I copied the original files from C:\ProgramData\MTA San Andreas All\1.5\GTA San Andreas to my E:\ Steam directory.
3) E:/ is already the new disk (used to be on D:\), the issue is still the same.
4) Thank you for providing the link. It used to crash without the mod installed and that stopped happening. So atleast I can play the game without the ENB for now.
Using Micras Registry-File (https://github.com/multitheftauto/mtasa-blue/issues/1103#issuecomment-849308970) and "Disable DVR1.reg", "Disable DVR2.reg" and "fullscreenfix.reg" seem to improve ingame performance (https://github.com/multitheftauto/mtasa-blue/issues/1103#issuecomment-1504249833).
5) I doubt that will change the behaviour but I'll try it anyway.
Because it's a different, not cracked version, I created a new MTA Diagnose: https://pastebin.mtasa.com/3932449706
It reports \audio\CONFIG\TrakLkup.dat, \audio\streams\BEATS and \audio\streams\CUTSCENE as non-standard files. That may be the case because it's the steam version. I did not modify them.
Inside the report I found several "CreateVertexDecl fail" reports. After unplugging one of my monitors, the mod works like a charm. It does not crash, no lags, no freezes. Perfectly running ENB-mod. Literally nothing, it performs great. I can tab out and click the game without it crashing.
May that be a GTA:SA specific issue or is it related to MTA?
Just created a new Diagnosis, maybe there will be a difference?
https://pastebin.mtasa.com/6886113126
Sorry for double post, no clue how to edit a post here, lol