For anecdotal data, I'm a big fan of Apollo Neuro. It's a small band worn on the wrist or ankle and vibrates to stimulate the vagus nerve. Similar effect to tapping on your wrist. The sleep mode seems to improve my deep sleep scores on my Oura ring. I haven't done any proper data analysis to confirm.

Apollo Neuro claims to have lab data proving efficacy: https://apolloneuro.com/pages/science

Even if it's more of a placebo effect, I still enjoy the benefits of devices like this.