Failed to initialize GTK - You're probably running Synaptic on wayland with root permission

The error message in the title should be of more help. LOL

Following this, is the description copied from youtube (where this video was uploaded first):

This is so utterly frustrating to be met with the following error (which is a hit and/or miss in solving) after upgrading (or going the route of a clean install) your system, only to find you cannot use it in any TTY (cli or text-only interface), just via GTK (the graphical interface).

I ruled it out using LMDE5, LMDE 6 (uses debian), debian itself 11 and 12) and ubuntu (latest available), including two other machines I recently updated, same thing. With or without root permission, it simply relies on GTK to function, or it refuses to run.

I'll type out the error right here:
Failed to initialize GTK
You're probably running Synaptic on wayland with root permission.
Please restart your session without wayland, or run synaptic without root permissions.