I had nextcloud 10 working following mis perry from you tube video
then all went to hell
curl https://download.nextcloud.com/server/releases/nextcloud-17.0.0.tar.bz2 | sudo tar -jxv
Internal Server Error
The server encountered an internal error and was unable to complete your request.
Please contact the server administrator if this error reappears multiple times, please include the technical details below in your report.
More details can be found in the server log.html/
I have the ugly servernexcloud.log too