Yes, this is all pre-release stuff!
You need to update the goggle firmware to get the headtracking data to the ELRS backpack in the googles; the ExpressLRS backpack in the goggles to send the headtracking data to the ExpressLRS backpack in your TX module; the ExpressLRS backpack in your TX module to send the headtracking data to the main part of the ExpressLRS TX module; the ExpressLRS main TX module to merge the data into it's stream, sent to the RX in your model; and finally update the ExpressLRS Lua Script in your TX16S.
It's a LOT to update and right now all of it is pre-release. Luckily its all backwards compatible. However it's not for the faint hearted!
It's a LOT easier to do it wired. Just update the goggles with the firmware and wire the headtracking cable from the goggles to the trainer port on your TX16S. This way you have to configure the TX16S Open/EdgeTX to pass the data to the R/C model, but that is a well documented procedure and not a new process at all. Painless360 has a video about the Open/EdgeTX setup for headtracking.
https://youtu.be/_p8_1v9-3D8
The wired headtracking is in the latest release candidate. 8.0.0-rc1
https://github.com/hd-zero/hdzero-goggle/releases/tag/v8.0.0-rc1
Note that the setup procedure for wired/wireless is quite different once outside the goggles. With wired the signal goes like this:
goggles -wire-> TX16S -> Elrs TX Module -air-> Elrs RX module -> Flight Controller/Servos
with wireless it goes like this:
goggles -> goggle Elrs backpack -air-> Elrs TX Module backpack -> Elrs TX Module -air-> Elrs RX module -> Flight Controller/Servos
As you can see the TX16S is only in the line in the wired version. There's no TX16S setup needed in the wireless version, you just have to setup the Elrs Tx Module with it's LUA script.