flatpak-system-update.service fails to start: Cannot autolaunch D-Bus without X11 $DISPLAY

[1player]

Dec 04 11:06:17 tranquility systemd[1]: Starting flatpak-system-update.service - Flatpak Automatic Update...
Dec 04 11:06:17 tranquility flatpak[423203]: These runtimes in installation 'system' are pinned and won't be removed; see flat>
Dec 04 11:06:17 tranquility flatpak[423203]:   runtime/org.freedesktop.Platform.VulkanLayer.gamescope/x86_64/23.08
Dec 04 11:06:17 tranquility flatpak[423203]: Nothing unused to uninstall
Dec 04 11:06:18 tranquility flatpak[423210]: error: Cannot autolaunch D-Bus without X11 $DISPLAY
Dec 04 11:06:18 tranquility systemd[1]: flatpak-system-update.service: Main process exited, code=exited, status=1/FAILURE
Dec 04 11:06:18 tranquility systemd[1]: flatpak-system-update.service: Failed with result 'exit-code'.
Dec 04 11:06:18 tranquility systemd[1]: Failed to start flatpak-system-update.service - Flatpak Automatic Update.

Looks like https://github.com/flatpak/flatpak/issues/3847

Of course it works when I execute the commands manually. I'm pretty sure it used to work months ago, and it's only recently that I find that my Flatpaks are not updating automatically anymore.