If you running Nginx, add this to your nextcloud.conf file:
location ^~ /.well-known {
# The rules in this block are an adaptation of the rules
# in .htaccess that concern /.well-known.
location = /.well-known/carddav { return 301 /remote.php/dav/; }
location = /.well-known/caldav { return 301 /remote.php/dav/; }
location /.well-known/acme-challenge { try_files $uri $uri/ =404; }
location /.well-known/pki-validation { try_files $uri $uri/ =404; }
# Let Nextcloud's API for `/.well-known` URIs handle all other
# requests by passing them to the front-end controller.
return 301 /index.php$request_uri;
}
Re-start Nginx and check if the warning is gone.