Choosing a domain in the selection menu, or setting a custom one, lets you access the games through a different domain. If your games show a blank page, or a blocked page, it is recommended to change your game domain to an unblocked one. Remember that changing your game domain will reset all of your game data until you change it back or load one of your save files. If you want to use a Custom Domain, you can fork the Assets Repo and host it, then enter your domain (When entering your domain, make sure it is only the domain you're entering, not including https:// or anything else | etc. myassetsfile.vercel.app).
You cannot host the assets repository using Github Pages as the build and deploy will most likely fail. Just a note that deploy time is more than 5 minutes in most web hosts, and some may take as long as 15 minutes to deploy. If you will be deploying, you will be deploying yourself, as we will not help you in deploying the assets repository.