Unable to change animation type from "humanoid" to "generic" in 2020.3.7f1

Hello, I bought some characters that came with Generic animations, but unity imports them as Humanoid.
Whenever I try to change them to generic at the inspector, they go back to Humanoid!
I also tested the animations at unity 2018, and they seem to work fine at the generic setting, but if I copy them to my unity 2020 project, they go back to humanoid again. It looks like unity 2020 refuses to convert them to generic :[
Anyone knows how to solve this problem?

P.s.: I tried to copy only the animations from 2018 to 2020, but that doesn't work either. What I wanted was to find a way to convert those humanoid animations to generic in unity 2020.3.7f1

P.s.2: The animation type is already generic. Only in unity 2020.3.7f1 I am unable to change from Humanoid to Generic