I recently upgraded a computer From Linux Mint 20 to Mint 21 with an in-place upgrade. I recently noticed that I can no longer open the "Software Sources" dialog. Online I saw some advice to try and open software-properties-gtk and observe the result. When I do this, I get an error:

Error executing command as another user: Not authorized

The upgrade could be unrelated to the issue, but I did find another person with a similar issue after upgrading here. However, unlike in that question, synaptic-pkexec opens fine for me from the command line (and GUI), and I don't have updates to apply, my updates are clean. I have, however found that mint-release-upgrade gives the same error if I try to run it.

Why can't I open these programs, and how can I fix this?


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