That's what I did. Just an esp32 relay board with a tiny screen and a knob. Then I put more esp32 sensors in each room to get individual temps, with HA logic to select which room the thermostat pays attention to. If HA dies for some reason it falls back to a local control and I'm back to the same situation as before, a thermostat that only pays attention to the temperature in the hallway it's installed in. All the boards were flashed with ESPHome.

It does feel hella jank, but it's pretty obvious from the tone of the text that the author is fully aware of that. He went through every available option in order from reasonable to jank and this is the first one that worked.

There's nothing wrong with jank as long as it's not going to burn your house down the way some of his other rejected ideas would have.