Okay, I tried now both. (Yeah, the problem first was, that I didn't uninstalled the old version.)
The MGC_6.1.013 was barely usable, the test.8.1 is better, but still far from perfect. Can't use Nightmode or Portrait, both have massive lags - I can't even take a picture. Normal camera and video...
Am I right, that *no-support-for-this-app-on-this-forum* will probably not working on my Mi8 EE, because I use the Stable Rom from Xiaomi.eu, which is by now just on Android 8? Is there a version for this too? Thx!