I bought a Garmin watch over Fitbit because it works with Gadgetbridge.

What is gadgetbridge and what do you get out of it?

Another person beat me to it, but it’s basically an open source app for wearables and other related devices. It aggregates all of my health metrics and made it so I never once had to connect my watch to Garmin’s cloud services. All of my data is just stored locally on my phone.

You can see the supported devices here: https://gadgetbridge.org/gadgets/