Garmin watches seem quite open even without that. I have all my data syncing to influxdb every 15min for a Grafana dashboard and it works great.

In background I also have Withings scale sync the measurements a couple of times a day to Garmin.

How do you sync the data out of Garmin? Something like https://github.com/matin/garth, or syncing directly from the watch?

Probably the reason why Garmin watches are well supported by GadgetBridge