I use Nextcloud and it is very dated and with poor performance in multiple areas.
I was expecting someone would come and make a more modern open source private cloud server in Go or Rust, but I did not expect ownCloud to do the rewrite. Nice!
It is fast, extensible and due to its status, many clients and apps can sync to NextCloud. At this point it is known enough, that it can replace sonething like iCloud for anyone looking to switch.
https://help.nextcloud.com/t/why-doesnt-android-client-uploa...
I am always running the latest stable version.
Phone sync is terrible (does not work properly), opening gallery view with a few images takes from 30sec to never, iOS app crashes frequently, there are all kinds of UI glitches, etc.
Almost all of these problems have been reported in their bug tracker, some of them have been there for years, but since those are not that relevant for their business customers, they don't really fix them.
That sounds like a positive thing to be honest.