Thanks @Johnex! Your link did lead me to the third thing, DNS encryption to be disabled and now getting the portal popup!
So, all good and not going to need custom firmware :slight_smile:

Just a note if anyone else having the ”issue”.

  • Disable all VPN connections in the router.
  • Disable DNS rebind protection. This is generally true but not for all portal.
  • Disable DNS encryption. In GL.iNet routers there are CloudFlare DNS.