It's on board ELRS ( built-in into flight controller ), not a separate chip. It uses SPI (think about it as an internal port) to talk with a flight controller, instead of a regular UART (think about it as an external port).
Big difference in terms of how you bind and work with them. Also I heard on a livestream that those SPI receivers cannot be upgraded to ELRS 3.X and are therefore at the end of their line, unless manufacturers create new boards entirely, or something like that.
I wasnt able to find the video. It was mentioned on FPV News with JB and ItsBlunty recently, but here is a link to the GitHub mentioning the SPI receivers in the notes: