I am using Ubuntu 20.04 with Gnome 3.38.0-1ubuntu1 (installed from PPA).
I moved /usr/share/themes to /usr/share/themes_backup. I also deleted $HOME/.themes, and checked that $HOME/.local/share/themes did not exist.
However, Gnome still boots into the default theme, even though it has been deleted.
How is this possible? Is the default theme backed up elsewhere?
NB. This question follows issues themes on both Budgie and Gnome, posted here (Cannot change themes after hard reset - Budgie Desktop - Ubuntu Budgie)
I also asked this question at Unix stackexchange, but without any response
(ubuntu - Default desktop theme still boots, after being deleted - Unix & Linux Stack Exchange)