Now when I try to access my nextcloud instance it understandably says that it is in maintenance mode. How do I recover from this?
You can deactivate the maintenance mode.
sudo -u www php occ maintenance：mode --off
or set it in
'maintenance' => false,
Thanks. How do I verify that the upgrade went through successfully?
Go back to the administration settings in Nextcloud GUI. Post details e.g. a screenshot.
Looks like it was successful. I can see the version as 24.0.4.