Same for me, unable to upgrade in any way, I get the same major versions error.
What I tried so far:
Uninstalling nextcloud using package manager, and deleting the rest of the install folder afterwards. Then I installed NC12 using the package manager and imported my config.php and data directory. Also imported the database as instructed in the documentation for a restore. Unfortunately the problem persists. There is not even a way I can get out of maintenance mode. The site always shows that it wants to upgrade.
I also tried to do as instructed here but without success. The problem is exactly the same.
Finally, I also tried to modify the version number in my config.php, but it did not change anything either.
The occ command gives the same error and stops the upgrade procedure.
Before upgrading, I always make sure to set the right permissions for upgrading: chown -R ${htuser}:${htgroup} ${ocpath}
Any help would be greatly appreciated!
I am on archlinux armv7, everything up-to-date.
Here the last stuff from my updater.log in the data folder.