I think it's worth taking a look back at X10 [0], the OG home automation.
Yes, it was primitive by today's standards with a very limited command set, but that command set was good enough for 90% of purposes and its simplicity meant that it was trivial to implement correctly and everything interoperated.
It didn't need an internet connection to function. It didn't even need a local server. Though you could have a programmable controller, the minimum viable setup consisted of having some X10-enabled device (such as a light socket), an X10 switch, and setting some DIP switches as configuration.
Yes, it was primitive by today's standards with a very limited command set, but that command set was good enough for 90% of purposes and its simplicity meant that it was trivial to implement correctly and everything interoperated.
It didn't need an internet connection to function. It didn't even need a local server. Though you could have a programmable controller, the minimum viable setup consisted of having some X10-enabled device (such as a light socket), an X10 switch, and setting some DIP switches as configuration.
[0]: https://en.wikipedia.org/wiki/X10_(industry_standard)