Finally, I put the rewriterule in the docroot of my apache2 server and now the warning disapears.
here is my .htaccess
#
# My htaccess @ docroot
#
Options -Indexes
#
# Wichtig für NC29.x.x
# https://docs.nextcloud.com/server/29/admin_manual/issues/general_troubleshooting.html#service-discovery
#
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteRule ^\.well-known/carddav /cloud/remote.php/dav [R=301,L,B]
RewriteRule ^\.well-known/caldav /cloud/remote.php/dav [R=301,L,B]
RewriteRule ^\.well-known/webfinger /cloud/index.php/.well-known/webfinger [R=301,L,B]
RewriteRule ^\.well-known/nodeinfo /cloud/index.php/.well-known/nodeinfo [R=301,L,B]
</IfModule>