Art Of Living’s course 1 Sudarshan Kriya offers breathing course which activates the vagus nerve. I have attended this course. It claims to reduce anxiety, depression and addiction. I have not practiced it regularly. Sorry to say that.

Here is that article:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3573542/

https://en.m.wikipedia.org/wiki/Art_of_Living_Foundation

I hope this helps. I wish you good luck on your journey to good mental health.

Just caution, don’t turn it up to much and don’t overdo it. More is not better. A style of it can be had cheaply with a TENS 7000 and ear clip set off of Amazon. You will find research and anecdotes to support your decision either way. That’s a truism that’s always been true but perhaps especially in this day and age of overstimulated people and an endless amount of content generators.

Ultimately if you think it’s working then it’s working.

A lower risk way is probably breathing techniques and meditation apps.

I'm using a Dolphin Neurostim VNS to recover from COVID-induced anxiety. I'm getting better over time, especially my sleep, so maybe it's working? I had really bad depression for a while too, and that's mostly cleared up. It's not cheap but it's an FDA approved therapy for a number of conditions.

It sends microcurrent (literally - millionths of an amp) through the two halves of the vagus nerve via the left tragus to the left wrist, and from the right concha to the belly. Each half takes about fifteen minutes.

When I started using it I had some weird moments where my heart would skip a beat, but I ramped up the treatment durations over a couple weeks and now the treatments are uneventful.

Supposedly it's much safer than TENS units which deal with currents that can overload your nervous system.

BTW, look into Silexan lavender oil too ("Calm Aid"). Supposedly better therapeutic outcomes than prescription antidepressants and anxiolytics, especially at 160mg doses.