owncloud 9 was installed before at a raspberry pi with debian jessie.
I removed ONLY the owncloud-* packages and unpacked the latest nextcloud 9 to /var/www/owncloud
The occ upgrade was successful, but even after a full reboot, it is only a blank page.
Need nextcloud 9 more packages?
Can I already upgrade to nextcloud 11?
Can you check you logfiles? There should be some information why you are only seeing a white page (Nextcloud-log in the data folder, but also your webserver logfile).
You need to have NC 9 running before upgrading further to NC 10 and then to NC 11.
Removing the owncloud packages also removes the webserver config files, I guess you have to set those settings again in your standard ssl config/vhost.
Check the admin manual installation instructions for proper webserver deployment: https://docs.nextcloud.com/server/9/admin_manual/installation/index.html
ok, I deleted any file, except the config folder and unpack the archiv again.
Something was missing at the apps folder.
I upgraded over nextcloud 10 to 11, but I could not find contacts or calendar.
Are these apps missing at nc11?
For me they show up in the organisation category of the app store.