Most people won't agree with this but... Amazfit. About as closed as you can get. It has (depending on the model) about as many features as you might want. Mine, the GTR4, is circular and gives a decent watch effect with a dark watch face and a leather strap. It has GPS, can pair directly to Bluetooth earphones and has some internal storage you can use to upload your music so you can use it offline. No SIM/eSIM though.

Back to the closed part: You only need to install their app and pair it to theirs during the initial setup, once. Following Gadgetbridge's clear instructions, you can then get the login token, pair with gadgetbridge instead and just uninstall the official app. It then becomes your trustworthy watch that never sends any data out, because it no longer uses the official app. Not just amazfit though, I'd suggest to go to their supported devices list (which is... Comprehensive by now), and carefully check if a device you are interested in is supported and to what degree. Gadgetbridge might look ugly but it's 100% reliable and privacy friendly.