Did you ever get this to work?

[PseudoDistant]

I have this very same phone (Well, it's not my main phone anymore, I mainly use a Pixel 8 now), and I've been experimenting with GSIs on this device.
Most GSIs I've been trying have some pretty nasty issues like not being able to set a password or not being able to swap from USB host to USB device mode, so I've been looking into trying to port LineageOS instead of using a Treble build.
Unfortunately, I have only built LineageOS on top of existing device builds (Updating 17.1 to 18.1, was simple enough), I'm not experienced in making builds from scratch.

The closest match to the hardware that I've found is someone having gotten Pixel Experience running on the Xiaomi Poco M4 Pro 5G, which I can't verify if it even works due to not having the Poco myself.
https://github.com/Xiaomi-MT6833/device_xiaomi_everpal

The issue here is everpal is based on the Dimensity 810, as opposed to the Dimensity 700 that austin is based on.
The chipsets are similar enough that I could probably port this with enough effort, but if your device tree works instead, I'd rather use that, since it's actually intended for austin.

Did you ever actually get this working in a build? Did you get a working recovery image?