Gonna shill Venstar's colortouch line despite not having any financial relationship with them. Only because I don't see anyone else mentioning them, and I've had good luck with them for the past ~10(?) years in multiple houses. They are AFAIK the only "smart" wifi thermostat that both provides a standalone local JSON API (https://developer.venstar.com/documentation/) , and have a pretty wide ecosystem of devices and supporting infra that covers as much if not more than what some of the larger players do.
They are pretty niche, so much so that it took me maybe a year of half-hearted searching before I found a smart thermostat that wasn't dependent on an internet connection. And of course there is a home assist integration/etc https://www.home-assistant.io/integrations/venstar/
Read some reviews before you buy them, or you might be surprised by the resistive touch on some models (which works fine with the UI), audible click when the relays go on/off (this is actually a big advantage in failure modes), and other features some people might not like.