Please refer to:
https://help.nextcloud.com/t/nextcloud-21-eine-hintergrundaufgabe-importierten-ssl-zertifikaten/109843/39
Link shows how to solve this issue by SQL dbadmin request.
Look at: https://ask.linuxmuster.net/t/nextcloud-update-auf-20-0-7-fehler-bei-pdf/6980/14
Add to .htaccess (regarding to your installation path):
Redirect 301 /.well-known/carddav /owncloud/remote.php/dav
Redirect 301 /.well-known/caldav /owncloud/remote.php/dav
Redirect 301 /.well-known/webfinger /owncloud/index.php/.well-known/webfinger
Redirect 301 /.well-known/nodeinfo /owncloud/index.php/.well-known/nodeinfo
Maybe it helps!?
God luck and regrads.