Legion client, so all Legion features are coded in, just disabled. For example, cross-realm mail - when entering the addressee name you will get autocomplete prompts for your characters on other realms, even though you can’t send mail to other realms.
It’s actually the shadowlands client since TBC pre-patch, we got RTX shadows at that time on classic, and that was a new feature for retail in the SL client
Patch 3.4.1 next wednesday with ulduar also updates the api to the 10.0 dragonflight api, so expect a bunch of your addons and other stuff to break. Hopefully the game performance doesn’t get worse, dragonflight client has been quite bad on retail so far