Comment 1 for bug 1890608

It looks like something is going wrong with loading addins, which I assume you had installed with a previous version of Pinta? On my Ubuntu 20.04 VM I was able to install an add-in and restart Pinta successfully, though. I'll try setting up a Mint VM and do more testing there to see if I can reproduce it.

As a workaround, does removing the add-ins from the .config/mono.addins/addins folder in your home directory allow you to start Pinta successfully?

Also, what is the output of running 'apt search mono-addins' in a terminal? Perhaps Mint has a different version of Mono.Addins that's causing some issues