Recently the relatively cheap and over the counter supplement
Taurine has been getting attention as a “Long Covid Effects” treatment

https://medicalxpress.com/news/2023-10-amino-acid-play-key-role.html

Earlier the simple amino acid Taurine got attention because the blood of children has ten times the concentration of Taurine than elderly people.

https://medicalxpress.com/news/2023-06-taurine-key-longer-healthier-life.html

https://www.news-medical.net/news/20230616/Does-taurine-deficiency-speed-up-aging.aspx

I started taking Taurine.
I have noticed unexpected and unmentioned effects:
all my fingernails are growing faster, thicker and stronger.

My left thumbnail used to keep splitting at one spot, and that has stopped, which was a welcome change