I think OP put a few restrictions they could relax a bit. I use Meross devices with krahabb's wonderful LAN integration (https://github.com/krahabb/meross_lan

I think OP put a few restrictions they could relax a bit. I use Meross devices with krahabb's wonderful LAN integration (https://github.com/krahabb/meross_lan https://github.com/krahabb/meross_lan). It requires a specific pairing process of the device, but not any firmware reflash. Relaxing an extra bit, one can flash many devices with ESP Home (https://esphome.io/ https://esphome.io/) - an excellent cistom firmware. Its only flaw is that the captive portal does not work well after an upgrade (something that is hanging in the bugs section and nobody cares)