Dear Ino,
I would recommend you remove the 2021.2.3 version of psychopy and then make sure you installed the Compatibility+ version of Psychopy 2025.x.x. Then if you look under settings/properties you’ll see a “Use Psychopy version” field. Select the version of psychopy you need from there.
If that doesn’t work, the way I addressed this issue in our lab is to create a new user login (User B) on your testing computer. Then make sure psychopy 2025 is installed onto User A’s directory. Then install psychopy 2021.2.3 on User B’s account in their specific directory. This way psychopy won’t be upset about conflicting libraries and python versions.
Issac