So... this is some random person give you reasonably well cited advice but: This made the rounds a few days ago.
https://blog.ncase.me/on-depression/
... and today this was published on pubmed:
https://pubmed.ncbi.nlm.nih.gov/41506004/
The summary of both together seems to be that vitamin D and omega-3 acids are extremely important for the well-functioning your brain, more effective than antidepressants with effectively zero side effects for most people, and a year's supply of both is about $60.
So I'm trying it out.