If you installed gnome-settings-daemon in the debian-11 template, and it didn’t work, you can try the following.
Edit /etc/X11/Xsession.d/25xdg-qubes-settings and remove the lines
if [ -x /usr/bin/xsettingsd ]; then
installConfigurationFile "xsettingsd"
installConfigurationFile "fonts.conf"
installConfigurationFile "Xresources"
/usr/bin/xsettingsd &
fi
If xsettingsd is started, you can’t run another xsettings manager, preventing gsd-xsettings from starting.