then want i give you this also to the hand,
i have run my nextcloud as sub behind my domain…
Take a look :
https://domainname.net/nextcloud
/etc/httpd/conf/webapps.d/nextcloud.conf
# nextcloud configuration
Alias /nextcloud /srv/nextcloud
<Directory /srv/nextcloud>
DirectoryIndex index.html index.php
AllowOverride All
Options +FollowSymlinks
Require all granted
Header always set Strict-Transport-Security "max-age=31556926; includeSubDomains; preload"
Header always set Referrer-Policy "no-referrer"
SetEnv HOME /srv/nextcloud
SetEnv HTTP_HOME /srv/nextcloud
<IfModule mod_dav.c>
Dav off
</IfModule>
</Directory>
Redirect 301 /.well-known/carddav /nextcloud/remote.php/dav
Redirect 301 /.well-known/caldav /nextcloud/remote.php/dav
like you see, have i bound in the “Header always set Strict-Transport-Security” also in, as well as “Header always set Referrer-Policy”
in your case should this be
Redirect 301 /.well-known/carddav /remote.php/dav
Redirect 301 /.well-known/caldav /remote.php/dav
because your sub.domain.com is in this case the root so “/” and .well-known/~ is the way to
“/remote.php/dav” so : "cloud.mydomain.com/remote.php/dav "
so must it named ^^
if this works, give feedback…
this could/should be pinned for “Apache-Configuration files”
or build up a Wiki !! 
best regards
Blacky