System Bridge might just be what you’re looking for.

Not sure if a Chinese app will offer more privacy.

Take a look at the Prusa Mini and Bambu Lab A1 Mini. It sounds like you want something reliable so I’d stay away from the ultra cheap stuff.

Home Assistant OS won’t support this board immediately, though I’d expect a beta to arrive sooner rather than later.

USB-C iPhone? You’re right, it is working.