Paul,

I googled a bit more and found out that many people have this problem since the latest big Mac OS update when Python 2.7.16 was removed from the OS. This problem is not just related to AFNI or caused by AFNI, as you already pointed out, but the problem appears with all kinds of programs that use Python.

One solution is to simply reinstall Python 2.7.16 (the version that came with Mac OS by default). For example, one can use the following solution using homebrew: [github.com]
Maybe this helps out other people in here. You don't even have to use miniconda then.

I used this solution and it everything seems to work fine again. Using the command "python -V" prints

Python 3.10.4

This means that my shell/terminal uses the current version of Python, i.e., it is linked correctlly. But it appears that AFNI internally somehow still tries to link itself with Python2, since the problem no longer appears once I additionally reinstalled Python2 on my system. As you know, I am not a professional on this topic, so this is just based on my assumption.

In case you know about an even cleaner solution (instead of using 2 parallel versions of Python on my computer), and if you have some further thoughts, please let me know.

Thanks,
Philipp