Same here. After update widget was visible in Wearable app, but wouldn't add to watch. Next morning widget was gone. Have updated all Samsung Health apps and restarted both phone and watch.
I have an LTE Watch3 and a S20+. I can get the ECG to work with the app on my phone, but I cannot find v02 max anywhere to measure blood oxygen. It is not in Samsung health. I have updated everything and all software is up to date. Not in health, can't add as widget. How do I add this feature?