Final update, got a second hand unit installed. Back to working normally.
I went second hand as I like the factory units, the physical off and volume button. Also the maps speed camera alerts, albeit way out of date and I know you can use Waze etc but no carplay with these head units.
$560 odd for unit
$280 install etc
My research for replacements found:
Most can't deal with the Harman Kardon amp, uses CAN bus for volume and turn on controls or something. A few android units were compatible though.
Every unit is left hand drive biased in the layout.
https://www.joyingauto.com/joying-9-inch-car-radio-for-subaru-forester-impreza-wrx-sti-2013-2018-google-map.html - the older 9" model with a physical button.
https://www.idoingstereo.com/products/Idoing9quotCarRadioPlayerForSubaruWRX2016-2021GPSNavigationCarplayAndAndroidAutoHeadUnitPlugAndPlay360Panorama.html - which most youtube videos are about.
Two interesting option were:
https://teyes.co.nz/collections/subaru/products/teyes-cc3-for-subaru-forester-4-sj-2016-2018-car-radio-multimedia-video-player-navigation-stereo-no-2din-2-din-dvd - meant to have a better menu/interface
https://aucarauto.com/product/aucar-tesla-style-subaru-wrx-2015-2021/ - tesla style if thats your think
The cars are pretty much identical. I think the tS gets like... heated wing mirrors, some slightly fancy dampers and an STI badge on the steering wheel.
It is a little bit odd that they don't offer a manual tS but that's the reality of most car brands and their extremely limited customisation these days.