Alkir try this. paste as follows
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTP_HOST} ^(.+).mydomain.com$ [NC]
RewriteRule ^ https://mydomain.com/ [L,R]
# Ensure the Authorization HTTP header is available to PHP
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
# Uncomment the following lines if you are not using a `public` directory
# to prevent sensitive resources from being exposed.
# RewriteRule /\.git / [F,L]
# RewriteRule ^composer\.(lock|json)$ / [F,L]
# RewriteRule ^config.php$ / [F,L]
# RewriteRule ^flarum$ / [F,L]
# RewriteRule ^storage/(.*)?$ / [F,L]
# RewriteRule ^vendor/(.*)?$ / [F,L]
# Pass requests that don't refer directly to files in the filesystem to index.php
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^ index.php [QSA,L]
</IfModule>
# Disable directory listings
...............