It sounds like more recent Shelly devices can work as BT proxies, and of course, nearly anything with a ESPHome-flashed ESP32s.
It sounds like there’s some options involving MQTT, but it doesn’t sound like that behaves like the normal BT proxy. What might I be able to install on a RPi, or a PC or an android device to function as a real proxy?
To be a true proxy it would have to be tailor made for HA to route the messages to the bluetooth API like the esp bluetooth proxies do. Since esp’s are low cost and working great, I doubt any one took the effort to create (and maintain) something like it on other platforms. I haven’t seen anything like it, so I do not think there is such a thing. Maybe there are esp emulators with working bluetooth out there?
Also found this, but it apparently requires an add-on I can’t locate to work as a BT proxy. Would love for this to exist in the HA app: HA Bluetooth Proxy | F-Droid - Free and Open Source Android App Repository