If you go to the devices menu there's stuff for older models as well. I haven't tried out the builds yet, but have seen reports around the Internet of other people using them with success.
Currently playing around with Android TV on a $20 disposable Walmart Onn-branded streaming box to see what apps and customizations are possible before taking the plunge and fiddling with on of my RPi 4Bs. Though you might want a Pi 5 for a 4K TV.
Long term goal would be to combine Raspberry Pi, reliable builds of AndroidTV which are downstream of either LineageOS, CalyxOS, or GrapheneOS, and then some kind of IR Receiver like the FLIRC and a remote control.
Custom ROM to drive the TV, no ads, no commercial partnerships. Root your TV.