"But it’s alarming how easy it is for smart device makers to decide that your property won’t work. There’s no easy solution to this problem. "
Uhhh ... yes there is. Use standard protocols or open the APIs. Every device that requires vendor-managed cloud control should be considered as having a limited lifetime, which could blow at any moment.
(I put my Dreo fans and Roborock vacuum in this category. i priced that into my initial purchase decision.)