That is awesome! Sometimes things are cached and do not display correctly right away.... or maybe it was the phase of the moon 😉
Also, the reason you were not able to access the favicon.ico from <URLroot>/portal/favicon.ico is because "/portal" is the web adaptor which works like a forward proxy redirecting requests to Portals internal web server. That URL returned a 500 error because favicon.ico is not located in the Portal internal web server.
Glad it is now working for you.