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