I tried all of the above. Modifying Cups did not work in Linux Mint 20, which is based on Ubuntu 20.4. Apparently, Ubuntu and Mint no longer use Cups for Printer discovery, but instead now use Avahi. I think it is a Systemd thing. Setting
enable-dbus=no in avahi-daemon.conf somewhat worked, but caused the print menu in LibreOffice to take a long time (...
I awhile ago faced the same issue, with Arch Linux (Not ubuntu) although,
today I had the same problem, wich was fixed (in my case) by removing pavucontrol, rebooting, and installing pavucontrol again, changing some configurations in the config tab, and it, for me - worked)
Hope this can be useful for the future.