That is helpful

1. Go to here
  https://github.com/rordenlab/MRIcroGL/releases/tag/v1.2.20211006

2. Download and install the new "which" variant 
  MRIcroGL_macOS_which.dmg

3. Launch from command line and tell me what you see from the command line.

Searching for AfniDir
Running command: /bin/zsh -l -c "which afni"
Result: 0 afni not found

Running command: /bin/bash -l -c "which afni"
...