OK, that solved something. I got the web interface telling me to upgrade:
App update required
Please make sure that the database, the config folder and the data folder have been backed up before proceeding.
I tried to click the update button, but it told me “an error has occurred”. I then tried to do the update via cli:
$docker exec -it -u abc nextcloud php /config/www/nextcloud/occ upgrade
Nextcloud or one of the apps require upgrade - only a limited number of commands are available
You may use your browser or the occ upgrade command to do the upgrade
An unhandled exception has been thrown:
TypeError: Argument 3 passed to OC\Updater::__construct() must implement interface OCP\ILogger or be null, instance of OC\Log\PsrLoggerAdapter given, called in /config/www/nextcloud/core/Command/Upgrade.php on line 97 and defined in /config/www/nextcloud/lib/private/Updater.php:87
Stack trace:
#0 /config/www/nextcloud/core/Command/Upgrade.php(97): OC\Updater->__construct()
#1 /config/www/nextcloud/3rdparty/symfony/console/Command/Command.php(255): OC\Core\Command\Upgrade->execute()
#2 /config/www/nextcloud/3rdparty/symfony/console/Application.php(1009): Symfony\Component\Console\Command\Command->run()
#3 /config/www/nextcloud/3rdparty/symfony/console/Application.php(273): Symfony\Component\Console\Application->doRunCommand()
#4 /config/www/nextcloud/3rdparty/symfony/console/Application.php(149): Symfony\Component\Console\Application->doRun()
#5 /config/www/nextcloud/lib/private/Console/Application.php(215): Symfony\Component\Console\Application->run()
#6 /config/www/nextcloud/console.php(100): OC\Console\Application->run()
#7 /config/www/nextcloud/occ(11): require_once('/config/www/nex...')
#8 {main}