Thanks for writing down the setupchecks-command! I had to run it with PHP 8.2 while on Nextcloud 27.
I’m using the test-version of the upgradescript from Github,
yunohost app upgrade nextcloud -u https://github.com/YunoHost-Apps/nextcloud_ynh/tree/testing --debug
From my log:
2025-01-08 21:44:14,857: DEBUG - Your data directory is invalid.
2025-01-08 21:44:14,858: DEBUG - Ensure there is a file called ".ocdata" in the root of the data directory.
I hit the missing .ocdata when upgrading from Nextcloud 27 on Debian 11 / Bullseye to Nextcloud 30 after migrating to Debian 12 / Bookworm.
For the next person hitting this: I used
# cd /home/yunohost.app/nextcloud/data/ && touch .ocdata chown nextcloud:nextcloud .ocdata && chmod 750 .ocdata
Something in the update changes the .ocdata to .ncdata, so after a failed upgrade, the .ocdata-file is missing again (as files are not backed up by default, and thus not restored to the situation before the upgrade)
After that I had an incompatible app (even though it was disabled; should have checked, not only updated the apps…):
2025-01-08 22:06:27,575: DEBUG - Error: App "Plain text editor" cannot be installed because the following dependencies are not fulfilled: Server version 27 or lower is required.
Thinks take much longer now, and there are all kinds of scheme updates to the database, so I let it run while I go to bed 
edit to add:
The next morning the upgrade turned out to have failed. Another app should have been uninstalled (which makes me think: if Nextcloud 30 can find out that an app is not compatible and that the only recourse is to uninstall it, why not give a warning that all incompatible apps will be uninstalled and log which apps got uninstalled? If there was an app that I really needed so hard that I’d like to stay on an old version, I still can revert to the backup from before the upgrade; not a YNH-issue, but might be implemented upstream)
Unfortunately, something left the restored Nextcloud 27 in a broken state. Not only Nextcloud itself is not working, also the Yunohost admin page for Nextcloud is broken (the page hangs in ‘getting info’).
Removing via CLI (yunohost app remove nextcloud) does work though, but after restoring the backup, Nextcloud is still / again in a broken state.
This is on a copy of the actual server, “no harm done”, but for now I’ll leave it at this and retry later with a clean slate.
Edit to add two weeks later: yesterday I tried again, on the actual server this time:
- apt update/upgrade
- snapshot server
- migrate YNH11 to YNH12: no problem (thanks to all involved)
- snapshot server
- upgrade NC29 to NC30: tried to find incompatible apps, NC turns out to check by itself, none found; no problem during upgrade (again, thanks to all involved)
- snapshot server
Two weeks ago I may have deleted the incompatible apps on the actual server as a precaution, but now it all ran without a hiccup.