Thanks again.
If I try to import a HUMANIK animtion instead of a MIXAMO, it says: “Mesh contains Hips bone as root but animation doesn’t contain the root track. Import failed.”
I looked into it and the skeletons are indeed different.
your animationfix works great, even though i had to speed up times 4 but i think its some blender settings.
TurboSquid characters are just 3d-Models you can upload to mixamo so they get automatically rigged there.
if i follow this tutorial: upload a character to mixamo to autorigg it, and now the Rokoko-Animations seem to work. But i have to download Maximo-Animations specific for my character.
It seems like Mixamo is using different skeletons for the ones you can download und the ones you upload->autorig->download.
this is so confusing, i think i dont really understand skeletons 
Cant thank you enough for this!
From now on I can continue by myself i guess.