I've been hosting Nextcloud since version 13 and have upgraded 7 times in total, to version 20 now. Never had a single issue upgrading. I'm hosting via Docker, so upgrading is as simple as pulling and starting a new image. Nextcloud takes care of upgrading tables etc itself and has never failed on me.

Same here. Upgrades always went without a hitch. I run it in Compose but the database is on the host (I much prefer that setup in general).

I think I've been using it since version 9 when I switched to it from whatever version of ownCloud I had been running some years prior (I'm not sure if their versions were still in sync or not) and I have the exact opposite experience. I have never used anything more stable. Database upgrades are always seamless (I've never had to even touch the db since install) and all I have to do is occasionally add some indices through the CLI when it asks me to. The automatic updater seems to also make some sort of backups and even if it doesn't, a standard mysqldump backup should be enough to restore pretty much everything. It even survived two migrations to new servers.

I run several nextcloud instances and never had the slightest trouble upgrading through several Debian versions and many Nextcloud releases.

I'm curious about this.

I used Nextcloud for a few years already and never, ever I had a corrupted DB in any of the upgrades.

I've also experienced upgrades corrupting my DB a couple times over the years, and once emptying the trash caused DB issues as well.

Less than 1 year and 3 "there goes my evening" issues so far, one which resulted in data loss.