We only needed a simple form, but we wanted to be fancy, so we used "nextcloud forms".
The docker image automatically updated the install to nextcloud 30, but the forms app requires nextcloud 29 or lower. No warning whatsoever. It's an official app, couldn't they wait that it was ready for NC 30 before launching it? The newsletter boasts "NC hub 9 is the best thing after sliced bread" yet i don't see any difference both in visual or performance compared to NC hub 2
Conclusion: we made our business to rely on nextcloud forms as a signup form, but the only reason we were using it was disabled who knows how many weeks ago.
Never upgrade to the latest and greatest of ... anything really, especially in production. Let others test it first, or as suggested already, have a staging environment where you test the upgrade first. I guess you can still downgrade nextcloud though, especially if you have a backup.
Are you using the AIO image? I don't know how well that works, but yeah, I absolutely hate automatic updates like that. I tried it once and I decided to use the plain "official but not supported" docker image instead, where I manage things myself. Never had an issue, and I can control which version I'm running, I can backup to wherever I want, using whichever system I want, etc.
AIO has a updater but it is manual by default
You need to enable automatic updates yourself, which.... Is done through a bash script you need to add yourself into the system crontab
And not only that, the instructions do say things could break and even suggests setting up backups for such