We have spent more than two days to try to get it running:
1) We have used the Ubunu snap setup
It was great: we could immediately log in.
The configuration was the 1st pain:
snap has only has a very rudimentary documentation. Just try to find the Apache directory and try to change a mariadb, apache or nextcloud property. We either were not able the right property name (missing docs) or we were in the readonly snap directory.
There are hacks to mount snap direcotries so we can write - but we're pretty sure our settings will be lost with the next update.
2) Manual Linux installation
Nextcloud has godd looking but useless docs: you will not find a simple step by step setup doc for e.g. the latest Ubuntu Server. The end? Use google to find 2rd party tutorials. Most will not work with an up to date OS like the latest Ubuntu. Some tutorials work nice, but you will get a very old, not supported Nextcloud V13. Update? Read the next chapter.
This is a real shame. The step by step instructions do not work, if you spend 1h and use google, you can get it running.
Of course, the 1st attempt fails, because you probably will upgrade from version 13 to 15. The Docs do not mention that its not possible to skip one version. Restore the backup, start from beginning. The tutorial talks about executing a phar file - which does not exist. Google solves the problem.
After 2h try and error, you finally get "success!".
As soon as we open the website, we get: Internal Server Error
"Check the log file", they write - but the do not mention the path to them. /var/log/nextcloud does not exists.
We spend some hours fixing well-known errors, unfortunately, the solution is not documented. Google is your friend: fix the 1st error, restart apache, google for the next error, restart apache, google for the next error, …
Once, Nextcloud displayed an explicit error on the login page and a non-clickable URL to solve the issue. Copy / Paste the URL - and guess what? "Page not found"
Nextcloud was our last pain.