BTW, I checked and I had two rubys installed. One was 3.0 and x86, the other was 2.6 and universal. Even if I manually removed the first one (it seemed to be installed with homebrew, but it wasn't on the list of homebrew apps), also from paths, nothing works yet. I tried to manually run the gem pristine commands, but they cannot write on the OS default gem.
Sadly I will have to find some other solution. Thanks for your answer.