The Galaxy Watch 4 and Galaxy Watch 4 Classic may be running Wear OS 3 under their One UI Watch 3 UI, but you must have a Samsung smartphone to use ECG and BP functionality. The new smartwatches are also incompatible with the Wear OS app, and they will not work at all with an iPhone or a recent Huawei device.
https://www.notebookcheck.net/The-Samsung-Galaxy-Watch-4-and-Galaxy-Watch-4-Classic-are-not-the-fresh-start-that-Wear-OS-needs.555007.0.html
And here I am still using a $20 Casio...
It would seem that, at least initially, Samsung is exerting its muscle on Google for the new Wear OS, and essentially getting what it wanted out of the deal: Samsung watches that now have access to the Google app store.
It will be interested to see whether Wear OS takes off beyond Samsung watches, and whether this would mean Google could exert some of its own muscle in the relationship.
I really hope WearOS flops and kills the Galaxy Watch line with it.
Samsung is really dumb to have ditched TizenOS and all their pros just to get some more apps on that Watch.