If you want to be sure all System Settings are set correctly, open the Settings tab inside the iPhone app, and click on "System Settings".

Then compare with this image:

"Notification" can be On or Off. Better to have On, so the app will advise you when an activity is ready.

"Allow Tracking" can be Off or On.

Then open the System Settings of your iPhone, and check the Health authorization. Refer to this article: https://waterspeed.crunch.help/en/something-is-not-working/heart-rate-or-calories-are-not-working

On Apple Watch, it is essential to check the System Settings/Workout inside the Watch and have every service activated, disabling both the power save and low GPS rate (if present). Also, in the System Settings/Display setting, be sure to have the Always on activated, if present.