- I already do exercise. Now, not especially, but it has never made a difference for me. A couple of years ago I was in a very good shape and I still had recurrent depression episodes.

- I don’t have any specific diagnosis regarding my mental health so I don’t take anything.

- Could you elaborate on the counseling thing? You mean like a psychologist?

The last point is very good. However, I’m not really “competitive”. I just want to live in peace. Thanks for your answer.

Psychologist or other therapist. If you're religious (you did suggest becoming a monk), a member of your religion's priesthood or analog can be helpful as well, especially if there's any sort of "moral crisis" component to this.

Along with medications, cognitive behavior therapy (CBT) understanding is very well distributed through therapists these days. I've found it to be very effective for my own depression and anxiety issues, to the point that, for me, medication is not necessary. Even if you go down the medication route, CBT is still a great addition to medication and talk therapy in general.

You also mentioned having "post COVID brain fog", it's good that you recognize that at least part of the issue is external to your own self (though not to your own body and brain). As frustrating as something like that can be it's important to remember that it's temporary. I've discovered that I experience a similar long term brain fog after receiving general anesthesia which led to some exasperation in the past, but with understanding I can at least work through it now after surgeries. I had a surgery last August and basically lost most September-November to my mental recovery, but not as bad as previous surgeries where I didn't understand/know this about myself.