But that wire has to end at a WiFi transmitter at some point, it won’t work purely over ethernet wire, for example.
Yeah, not sure about that since those devices in question, where I’ve used it, have some Wi-Fi somewhere. I just remembered that there has been something done to provide it over a wired connection, but the device would have been wired to an access point. My specific use case was an Xbox wired to an AP and casting wirelessly from my laptop. So there is a wireless hop in the mix.
Very few vendors have bothered to include it, mostly the Chinese low and mid-tier device manufacturers. But it is not widely supported since, I want to say, circa 2017.
It was standard in Android. The only time I had ran into a situation where I haven’t had it was Google Nexus 6+. I haven’t tried a lot of different OEMs, but OnePlus and Microsoft have (had) it for sure. Samsung I have used their Smart View service, but I thought it was Miracast with Samsung specific extensions. Meta Quest 2, I was surprised seems to only work with Chromecast. However that suggests that you may be right. Most of my devices have support, but not all do.