I use Nextcloud privately on shared hosting, non-critical, non-production. Mainly for fun and keeping in the loop.
The web updater for 12.X to 13.X ran through and now I have a beautiful white screen. No access at all.
What can I do to find the problem?
… Look into the logs and check the latest error messages 
You can post your logs here as well and we try to assist. Most important is the nextcloud.log (placed in your data directory). Depending on the information we find in nextcloud.log we might need to take a look at the web server error log and the output of the browser debug console could be interesting, too.
Furthermore provide server details please. The software and software version you are using (web server, PHP, …)
Thank you very much, I will look into that.
Meanwhile, the mobile app says “server in maintenance mode”. Would you expect that to be true and is that an easy switch to flick?
Hi,
It is difficult to say, because I know nothing about your server, how you updated, if something went wrong during the update and what?
So, it might be possible that the server beeing in maintenance mode is somehow expected and normal.
Disable the maintenance mode and enter your webserver as admin user again, to see if the update was successful. To disable the maintenance mode, login in via ssh, change dir into the nextcloud directory and there into the “config” directory. Open the config.php and search for the line with “maintenance”. Change the value behind from “true” to “false”. Then enter your server via browser.