I think there are supplements which can be helpful for auDHDers/ADHDers but I would anticipate fairly marginal improvements except where there's a major deficiency or where the marginal improvements are enough to nudge you from the surviving threshold and into the "managing life" zone.

Iron is a good one, especially if you menstruate or you have a restricted diet/are veg. Low grade anaemia can fly under the radar and exacerbate executive dysfunction and energy levels etc. It generally takes a while to really kick in so try to keep on it at a regular/semi regular basis if you want to see if it provides you any benefit. Take it with vitamin C for absorption.

Magnesium is the next one on the list. Our diets are generally pretty low in magnesium these days. The anecdotal reports are that magnesium improves focus, mental clarity, reduces anxiety, and improves sleep. I've never really looked into the different forms of magnesium properly and I'm more than a bit skeptical about how some forms are touted as being better for this or that symptom, although I'm sure that some forms are more bioavailable than others. If you take iron supplements they tend to cause constipation but you can balance that out with magnesium oxide, which has a laxative effect.

Zinc can help with blood sugar, like magnesium, and it can help with neurological function if you're deficient in it.

B vitamins, especially B12, are important for mood and if you have a restricted diet or you're veg and you don't consume small mountains of nooch then it's a good thing to consider supplementing.

This is a bit of a hot take but I am of the armchair expert opinion that what is considered acceptable for vitamin D levels is too low. Vitamin D is a hormone and it's essential. Unless you eat a lot of organ meat, I'd recommend supplementing Vitamin D even if you get a lot of sun exposure. If you are sedentary or you don't get much sun then I'd recommend it even more.

If you're veg then creatine supplementation can have a marked impact on brain function and I'd recommend this especially for that demographic.

Can't speak to lion's mane but you can get it cheap at asian grocers if you know what you're looking for.

I'm more than a bit dubious about the supplement industry and it's so fucking unregulated that it drives me to distraction. Be very cautious about anyone selling you proprietary blends or some sort of special, rare form of vitamin that only they provide.