Update: I tested the laptop running Linux Mint when I still had GTK 3.24.24-4+deb11u2~mr6 installed on the test PC. I thought being able to print from the laptop running Linux Mint was always possible, but I was wrong. When I reverted to 3.24.24-4 on the test PC, I was no longer able to print from the laptop either.
Of course, this is a separate bug, but I thought I should share this info here to make it clear that it was a side effect of mr6. Jaycee
