With Bluesky your handle or username is actually a domain, and in fact you can change your handle to be your domain, assuming you have the ability to add DNS entries or files to the site. It is worth reading How to set your domain as your handle - Bluesky for some details on this.
It is worth highlighting that Bluesky uses the AT Protocol, which they developed, see AT Protocol - Wikipedia and Protocol Overview - AT Protocol for more details.