The brain is a very energy hungry and nutrient hungry organ.  It uses up to 10 times more energy than the rest of the body (at rest), or 20% of the energy supply.  Therefore, it makes sense that it is very important to feed it properly. Here is cutting edge information about how diet can improve mental illness:

Home - Chris Palmer, MD - Mental & metabolic illness (chrispalmermd.com)
Dr. Palmer discuses mental health issues as having a metabolic cause (energy production problem in the brain), which is a new way of looking at mental illness.
Psychiatric conditions helped by keto diet

It's also possible that simply adding MCT (medium chain triglycerides) can help:
Use of medium chain triglyceride (MCT) oil in subjects with Alzheimer's disease: A randomized, double‐blind, placebo‐controlled, crossover study, with an open‐label extension - PMC

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More information about the importance of micronutrients (vitamins and minerals) and mental health:

 The Better Brain:

https://thebetterbrainbook.com/
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Depression may be caused by inflammation.​

Among supplements that you can discuss with your healthcare provider, one of the safest and most effective is L Theanine (naturally occurs in Green Tea), which can help with anxiety, mood, and cognitive/focus:

https://thewell.northwell.edu/healthy-living-fitness/l-theanine-anxiety

https://pubmed.ncbi.nlm.nih.gov/31758301/
https://pubmed.ncbi.nlm.nih.gov/31623400/
https://pubmed.ncbi.nlm.nih.gov/27396868/
 

Adaptogenic (countering stress) support from Red Ginseng

A unique form of Ginseng called Botalys in Thorne's Ginseng Plus was used in a clinical trial which showed improved mood, stress resilience, focus, sleep, and memory.