Could be dangerous to post such crap - man will start loading up their systems, “just in case” and suffer side effects that are yet unknown.
We should not censor because some people might be stupid.
Most of these supplements have no real effect, but their use, for a few days is harmless. If you or somebody you know has an issue, there is little cost to trying a supplement for a few days, and seeing if you see any difference.
Most of these medical issues, IMO, are originating in the gut, where some bacteria is producing something which either triggers inflammation, or has some neurologicaal effect as an adaptation to try and exploit the enteric immune system, but it bleeds out into the blood and affects things systemically.
To that end, different vitamins and minerals can have an effect, just by altering what microbes are getting fed or not in the gut, and by altering gastric transit times.
All of that is way beyond research however. But people do have the very best, fully customized laboratory right in their living room - their own body. If you are definitely on the path to ending up with full blown dementia, try a supplement here and there, and see if you can feel a difference. Magnesium may be one of the most powerful, just because it can enhance gastric motility. B vitamins can get deficient, and I think the trace mineral supplement from Vitamin Shoppe, which has a good shot of lithium, can be helpful in cognitive issues as well.
Other stuff, SAMe, Phosphotidyl serine, fish oil, NAC NMN, NR, meh, there is no harm in trying it and seeing. Don’t triple dose, most of these things will probably have 80% of theeir effect at 50% of the dose.
IMO, the best possible thing anyone with these issues could do though, and the thing which I saw have the most dramatic effect in a relative with cognitive issues, is Traditional Chinese Medicine. I watched somebody completely out of it, become completely normal, to the point they had no idea why they were repeating the things they kept saying when screwed up, and it was done just off acupuncture alone.
The only issue with that is there are people doing it who are not good, and there are complete masters who will change your life, but you often just need to go to place after place until you find a master. Oddly enough the real masters are often the guys doing in in some weird hole in the wall, where you walk into a chinese hair salon, and the stylist points to you some back closet, where the guy is sitting at a desk that is falling apart. But that dude will be like an above-Einstein-tier genius who will take one look at you and even know stuff which happened to you in childhood, and see how it still manifests in how you think and hold yourself today. They can he really weird that way. But often even just an american-trained one with only half that master’s ability can help a lot, and a lot more than any supplements.