The nice thing about my Mitsubishi Heavy Industry units is I've got a bunch of MHI-AC-Ctrl[1] modules tucked into them talking to the service interface with Home Assistant. The neat thing is it doesn't just control it, it also makes all the internal sensors and codes available.
What I think we really need to do though is make publishing these control standards mandatory under right-to-repair laws - no one should need to be reverse engineering them, you bring a product to market you have to provide the complete spec for it's software interface and data.
Do that, and I bet we'd find in a few years every new appliance would support a common serial port standard and come with a code page in the manual for it (ironically the prevalence of Tuya-smart stuff has come very close to making this happen, but they go to absurd lengths to lock you out of the wi-fi microcontrollers).