@ramrod
Garmin Fenix (and a lot of other models) have a Breathwork activity, which includes around 5 different exercises. The exercises are guided by vibration (only issue is that sometimes you can barely feel it, as they alter the vibration depending on whether its an inhale, exhale or hold). The range from 5mins to 16mins; only pity is that you cannot create your own plan and sync it.
Measures Stress (HRV) impact, respiration rate (not sure why as not your normal rate, but useful to see if you are syncing correctly according to the planned breath rate, stress, and HR (SPO2 isn’t recorded - as per other comments - though I suppose you could take a manual reading prior and post activity).
If your stress gets too high you will get a notification and suggestion to run a breathwork activity. Personally I tend to run them prior to bed, as do find it reduces my time to fall asleep, and also have better stress levels during my sleep.