Since upgrading to Linux Mint 20 Gmusicbrowser will not launch. No windows open. Is there a fix for this problem?

Yes, it's because I still haven't made a new release, sorry about that. Either the package was uninstalled or it's just an old bug.
You need to use the git version, the last gtk2 version is in this branch https://github.com/squentin/gmusicbrowser/tree/v1.1.x or you can switch to the gtk3 beta version https://github.com/squentin/gmusicbrowser/ you just download a zip with the green button, unpack somewhere and run, as there is no compilation (if you don't care about translations).

Hello,

On Ubuntu 20.04, this is what I get when 'Edit filter' is selected in the gtk3 version from git:


LOG **: Name com.canonical.AppMenu.Registrar does not exist on the session bus
*** unhandled exception in callback:
***   Can't locate object method "can_default" via package "Gtk3::Button" at /opt/gmusicbrowser/gmusicbrowser.pl line 8007.
***  ignoring at /usr/share/perl5/Gtk3.pm line 572.
*** unhandled exception in callback:
***   Can't locate object method "can_default" via package "Gtk3::Button" at /opt/gmusicbrowser/gmusicbrowser.pl line 8007.
***  ignoring at /usr/share/perl5/Gtk3.pm line 572.


Quote from: Edmond Sicard on August 17, 2020, 13:20:31
Hello,

On Ubuntu 20.04, this is what I get when 'Edit filter' is selected in the gtk3 version from git:

Fixed in git, thanks for reporting it.