Nextcloud malfunction: Cannot write into "config" directory!

Nextcloud is returning

Error

    Cannot write into "config" directory!

    This can usually be fixed by giving the web server write access to the config directory. But, if you prefer to keep config.php file read only, set the option "config_is_read_only" to true in it. See https://docs.nextcloud.com/server/28/go.php?to=admin-config

for access to urls like https://nc.torproject.net/apps/files/. Screenshot: