Can open settings in Linux Mint only using the terminal and when logged in as the root user

I was facing the same issue, searching on the web I found this post that solved to me. I had to install Pillow again and everything back to normal.

 pip install Pillow==2.7.0

hope it helps you to.

Using strace, I saw cinnamon-settings failing to load libfribidi.

/usr/local/lib/python3.8/dist-packages/Pillow-8.3.1-py3.8-linux-x86_64.egg/PIL/../Pillow.libs/libfribidi.so

I solved the problem by installing the FriBidi development package (libfribidi-dev) and building Pillow 8.3.1 from source. This includes Fribidi in Pillow. I then moved the existing Pillow out of the way and installed the one I built.

Trying to copy (symbolic link) the system's libfribisi.so where Pillow expects it did not work.