Apache returning wrong Location header
HTTP_HOST refers to the Host: header specified, so your configuration works as expected based on what you're telling it to.
If you want to, you can either strip away the port, or specify another by matching it and using a backreference:
Remove port and default to https:
RewriteCond %{HTTP_HOST} ^([^:]+)(:[0-9]+)?$
RewriteRule ^ https://%1%{REQUEST_URI} [R=301,L]
Change the port to something else (8443 here):
RewriteCond %{HTTP_HOST} ^([^:]+)(:[0-9]+)?$
RewriteRule ^ https://%1:8443%{REQUEST_URI} [R=301,L]