Basically any Fossil / Skagen (they're the same thing) Hybrid (meaning e-ink) watch will work with Gadgetbridge. I personally have the Fossil Machine Gen 6 Hybrid which works great. Ignore the 'Alexa' bit, that does nothing via Gadgetbridge (and in fact you can just flat out remove that 'app' in the GB app). Heart Rate and Message/Notification/Call control functions all work fine. Step tracking works, but sleep tracking does not (Fossil doesn't have it done on the watch, it's done in their app, so until/unless GB replicates that functionality it won't work).

I use the Fossil Collider HR with Gadgetbridge and it's pretty great. Three are some downsides though:

• The set-up is a little bit of a hassle. You need to get the Collider's secret key, and that requires installing a jailbroken version of the Fossil app
• Any changes you want to make to the watch display have to be made in the Fossil app, which means you have to install that app and do a bit of a runaround whenever you want to change something

But aside from that, it's been a good year with my Collider HR and Gadgetbridge