What you are seeing here is a lot of people trying to use it as a file synchronization tool, and discovering that it's bloated beyond reason (because well, it's a file-sharing/collaboration tool) and the file sync functionality isn't even as good as you'll get from specialized tools.
The root problem is that nextcloud started as a file sync tool, and moved into other niche, and never bothered to communicate it.
I made the mistake of recommending it and setting it up for my 10 person team earlier this year and it has only been constant headaches.
Reporting bugs to GitHub is especially frustrating because the devs will just discard them, regardless of how well documented and reproducible they are. There was a mess with its Postgres connection pool where it would quickly run out of available slots if you used Collabora, the Google Docs clone, the devs rejected the bug reports without a second thought although there were many users who reported the problem.
This last hour I've been fighting it trying to reset a user's password, it says that it "cannot decrypt the recovery key".
I check whether the recovery key is enabled for that user, it says "Recovery key is not enabled".
I check whether encryption is enabled, it reports it as "false".
It's by far the flakiest piece of software I've used in 2023.
Since then, I've been running an always-on Syncthing instance as a "cloud hub" and that's been great, though I doubt it would scale well.
I have used Nextcloud at home for years now without issues and we also used it at a large university where it worked just fine (from a user perspective; I don’t know if it gave the administrators nightmares). I do agree that they should invest more time in polish and stability and less in swanky new features that many won’t need, but that would not lead me to discourage anyone from using (or at least trying) Nextcloud.
Seafile is a close call if it gets more attention to remove rough edges and a bit more feature but interface looks more polished.
The just working part, at least for me, are the calendar and contact plugins. Never had any issues with those. File sync with the desktop client works mostly fine on Linux where I use it most of the time. However, I've run into issues with it on Windows. Using the automatic bandwidth limit for example might cause Explorer to freeze. [1] Also forget about the automatic upload feature in the Android client, I switched to FolderSync for a reliable experience.
I've managed to get OnlyOffice working, Collabora Office previously broke for some reason. However latest upgrade also broke OnlyOffice. The solution for this is to put the secret and authorization headers into config.php in addition to the OnlyOffice plugin settings. [2] No idea why, but that is a thing.
My Nextcloud runs as a normal PHP application and I haven't had any issues with upgrading yet. Going from, I think, version 23 on Debian 11 to 27.1 now on a different machine running Debian 12 since I started using it.
Maybe I should find something more focused on file syncing, but the all-in-one approach of Nextcloud and its various plugins makes trying some new services very easy.
[1] https://github.com/nextcloud/desktop/issues/5031
[2] https://github.com/ONLYOFFICE/onlyoffice-nextcloud/issues/60...
It has a lot of the same features, and generally seemed a little more stable. However, it was a little more painful to configure, and has a few unique terminologies you'll have to get used to. Also it's UI does load faster than Nextcloud, but once loaded, it is a little less snappy.
For the user downloaded client, I found that it works, but is a little less convenient than Nextcloud (no Automatic pinning of the folder, no partial downloads to save space)
I can't attest to how well it runs currently, as I haven't used it for a few years, but I used it a couple years ago and it was pretty solid