@Poney70
Sorry was a typo. Is 20.1.2 on my Mi9T PRO. But doesn't work. Very strange, because you told me, it works with your 9T PRO (or do you use the "non PRO" Version?).
Yes i used the "Hide Magisk feature" before. Maybe this causes the problem? I'l try to "uninstall" Magisk completly and try again to install it fresh.
And thanks, but i know there is no need to install the manager sperately. i think its "over" from last install.