In summary: Manganese is an essential nutrient and too much will kill you.
On one hand we have people exposed to manganese is the air from industrial processes. These people definitely get Parkinson’s like symptoms, and in the aggregate score lower on various intellectual tasks. Monkey infants on soy formula (which has more manganese than milk based formulas) had mild neurological effects, so you can take in enough from food alone to be dangerous.
On the other hand, manganese superoxide dismutase is the only thing keeping your mitochondria from melting, and it does several other things besides. So we can’t just throw up our hands and say “no more manganese”, we have to actually figure out a safe level.
The World Health Organization has set the No Observed Adverse Effects Level at 11mg/day, based on the observation that some humans naturally get that much through their diet. As mentioned previously, we know you can get manganese poisoning through food alone, so this is not very reassuring to me.
The most comprehensive source I found on this was this thread on the soylent message boards (they cite several of the same things I did above, all correctly, so I trust their work ). According to their sources, most adults already eat enough Manganese to meet the RDA. I don’t want to put too much stock in the RDA, because neither I nor they could find out how the FDA (or the Linus Pauling Institute) set it. However even if you accept the number, if people are already getting it through diet, and too much is toxic, it doesn’t belong in a multivitamin.
This is worrisome enough to me that I’m tossing my multivitamin and focusing on getting individual missing nutrients through specific supplements (if anyone knows of a balanced B supplement, please let me know). It’s not so bad I’m tossing my protein/vitamin powder, because it has a lower volume of manganese and I don’t eat much at a time- however when it’s gone, I’ll probably switch to a straight protein powder.
Aceso Under Glass 
If you want vitamin B, a decent way to get it is to just mix some nutritional yeast into food you would be eating anyway. A little bit disappears into chili and can add a little bit of savory nuttiness to a wide variety of vegan food.
Alternatively, if you are not a vegan, have a nice steak once a week and you’ll be fine on vitamin B.
Having read only the safety section of the first link, I’d treat Mn-as-inhaled differently than Mn-as-ingested, since “Unlike ingested manganese, inhaled manganese is transported directly to the brain before it can be metabolized in the liver (35)”.
On ingestion:”most nutrients will generally provide 2 mg/day”, which, maybe even that is too much, but even if it is, it seems much smaller than the purported “20 mg/day” provided by some vegetarian diets, and yet “Manganese toxicity resulting from foods alone has not been reported in humans”. Like, maybe the neurotoxicity from ingestion is just too small to be noticed at those scales yet, or people haven’t looked hard enough for it yet, even if it’s present? Personally, I’m betting against that, so I’ll keep taking my multivitamin and eating a veg diet.
(I haven’t looked at the other links, and am not mentioning stuff that’s less relevant to healthy adults, like Mn in formula or in IV drips).
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Oh, and *entirely separately*, I’d wanted to mention on https://acesounderglass.com/2017/12/04/that-guy-lives-in-all-of-us/#comments, on which commenting is closed:
“conscious talky part” is a neat label for it, and I’ve seen it called “self”, “PR part”, “ego”, and “that part that Buddhists and Stoics believe you should stop thinking of as containing/being ‘you’ if you want to ditch the emotional pain that comes from dissonance between your identities and the world”–but it didn’t occur to me until very recently that these were all the same thing. Idk how to actually go about the process of disidentifying with this part, other than that maybe mindfulness helps, perhaps by “show, don’t tell”-ing you that “you” aren’t at all the same as the “omg I got a bad grade I’m a bad student ow”-type feeling, or even the part of you that houses that feeling, within your mind.