I have an Amazfit GTR 2 which works well for me. The trick that I found is, you can actually use their official app to get the most features, and then just deny internet access, so that they cannot spy on you. Otherwise, it also works well with Gadgetbridge, which is a really nice app. In general I can advice to get one that works well with gadgetbridge!

I wondered, is the per application network toggle grapheneOS specific? I also recently discovered it and its so nice. Was a bit shocked when I red some indications online that its not a normal android feature?

Gitlab is pretty good. Also a bit shady sometimes, but overall very nice and easy to get by with the free plan