I have the same setup, but on a HP N54L Microserver. I tried a cast to my Gen 1 Chromecast and it worked fine with my own https URL. I’m not using NabuCasa yet.
Can I ask how you have things set up? I am using docker images of nginx reverse proxy with duckdns to access home assistant core via https but when I enter my url at the authorization website the authorization redirect simply times out when I’m on my home network. Interestingly the authorization website works on an external network but the login is automatically aborted. I assume that is a security feature of the home assistant cast api.