The issue is pretty simple: as the Mac VPN client is licensed as a full Endpoint client, it includes a desktop firewall.
It is a mandatory component that cannot be removed.
By default this firewall blocks all incoming connections.
This would probably also impact Chromecast usage.
In Global Properties, you can configure the state of this firewall for all users.
Once the user connects to your gateway, the configuration of this firewall will be updated.
If you want something more granular than here, you will need to configure a Desktop Firewall policy.
This can be enabled by ticking the "Policy Server" option in your gateway object, then a Desktop Firewall policy can be added to an existing policy package.