I have an Enduro 2 (similar to the Fenix7x) and always use the chest strap for sports (jogging and cycling). The strap records interesting additional data and the heart rate data is much less susceptible to interference. The watch alone is sufficient for hiking.

The chest strap is more precise than wrist-based measurement. This chest strap also allows you to measure, for example, the ground contact time when jogging or the distribution between your left and right leg or how much your body moves up and down when running. However, I never wear a chest strap for hiking. If you are only interested in your heart rate and you are only jogging as a hobby, you don't need a chest strap. It is helpful for serious training.

I always use the belt, especially in 🏃 It's much more precise, especially during splits, and there are additional measurements: left/right balance, ground contact time, etc.