Hello @townie-woods
Thanks for the post! The first thing I recommend is making sure you have granted Strava consent to process and store your health-related data which includes heart rate data. If you'd like Strava to collect and process health data for future activities you can change your permission settings before your next activity recording.
Secondly, it sounds like you're recording with a Samsung Galaxy S21 Android phone, using the Strava App, is that correct? If so, you'll need to connect a compatible heart rate sensor to record you heart rate.
Instructions on pairing a HR sensor to the Strava App
You also mention the you have a Watch 5. If you have the Samsung Galaxy 5 watch, you can use the Strava WearOS App to record activities on the watch.
I hope that helps. Let us know if you have more questions.