I'm sorry but Nextcloud is getting a bit of an unfair shake here. I recently got a raspberry pi 4 and installing nextcloud on there wasn't rocket science: https://smalldata.tech/blog/2019/07/12/setting-up-a-raspberr...
In fact the biggest issue that I faced was that my router did not support NAT loopback which led me to using the pi for DNS in order to be able to use my "private" cloud.
Nextcloud is an open-source dropbox and is written in PHP. It can be very easily installed via docker and is quite mature at this point with a rich ecosystem of 3rd party apps for functionality other than file sync. Big props to the folks working on it!