Interesting the newer Xbox controllers can connect over Bluetooth with windows 10, but I found it much flakier than using their dedicated wireless adapter (which I guess works much more like the hardware in an actually Xbox)
Yes, the Xbox Series controllers are fully interoperable with the Xbox One, which they wouldn't be if they switched to some other technique.
Actually I think they switched to just bluetooth now, or at least the new ones can connect to my computer/phone just through bluetooth without an adapter (the old ones did require one though)
The third revision of the Xbox One (1708, doesn’t have the glossy plastic piece at the top where the Xbox button sits) added Bluetooth support. The consoles and the Xbox Wireless Adapter still use the “Xbox Wireless” (basically WiFi Direct), however.