Bug#941782: Excerpt from syslog

[Jeremy Bicha]

Thank you for taking the time to report this bug. The problem is that
gnome-desktop3 3.34 migrated to Testing before gnome-shell 3.34 did.
gnome-desktop3 should have had a Breaks against older versions of
gnome-shell.

I suggest you try to install gir1.2-gnomedesktop-3.0,
gnome-desktop3-data, and libgnome-desktop-3-17 from Debian Buster to
fix this issue until gnome-shell 3.34 migrates to Testing. Of those
packages, gir1.2-gnomedesktop-3-0 is the most important one since
libgnome-desktop-3-17 is probably still installed on your system.

Jeremy