I wish I knew all of that tbh!
It's generally a combination of tastes/textures - I really cannot stand the texture of most meat, the tougher/stringier it is, the less likely I can manage it so for example, I cannot eat steak (I have tried on multiple occasions) however I can do minced beef and I can do certain sorts of burger... I even got to a stage where I could do quite thick juicy burgers that are pink in the middle which I never thought I would..
But thats purely the texture - on top of that is the flavour! I really need it to be predictable, so McDonalds would win over 'lovely juicy home made minced steak' burger, because I know exactly what I am getting with McDonalds... the home made one might be quite mildly beefy or it might be really overly gamey and beefy.. and that'd be a nope!
This is the reason so many kids end up on bland, beige food and junk food - it is uniform and predictable. A bag of Quavers will be the same no matter where you are, what time it is, who gives it to you - a tangerine or apple will not be.
The 'nope' when it happens is ... weird. I can't swallow it. Even if I can bring myself to put it in my mouth. It turns to cardboard and I physically cannot get it down. Attempts to push myself result in crying, gagging and vomiting (and i am talking about pushing myself, alone, no one else there, in private!).
Because I am an adult, I don't fear food generally - I have control, so I won't ever be in a room with people eating fish, or meat on the bone, the smell/sight of which makes me gag. I don't have the pressure to try stuff so the fear is no longer there - it was HUGE as a child because at any moment someone would attempt to pressure me/bully me/coerce me to try things... and then be abusive in response to my reaction (my parents mostly).
It feels safer and therefore I am much more likely to enjoy what I eat, if I can stick to the safe foods... but randomly safe foods become unsafe sometimes. For ages I could eat Morrisons Potato Crispies (tater tots) - then over night, nope, ick, I would rather go hungry, can't get them down. Did they change the recipe? I don't know!
Having a basis of safe foods to rely on, I can then try to add in other things - so with the current basic diet, I am trying to add a finely chopped salad every couple of days and thats going ok (and is something that was a former safe food, so is a good bet. I didn't go off it, just half the ingredients were out of season/stupidly expensive.)
I do also have other sensory issues, and if they get overwhelming I suspect that sticking to verrrrry predictable, uniform, bland foods helps me cope.
It also seems to go in phases, so I had a phase of plain pasta with a bit of either olive oil or butter, some pepper and a TINY bit of cheese (not to the point it melts though, ew).
Then I went right off that, haven't even had cheese for about six months (unheard of for me, cheddar has previously been a safe food for over 30 years!)...
If I get very stressed I can go right off absolutely everything and that is hell, being starving hungry, hungry to the point of physical pain, but unable to find a single thing you can eat. Fortunately I am fat enough that its never going to finish me off and it's never happened for more than a few days.
As a kid - I was weaned onto pureed whatever my parents were having, after being breast fed until 8 months ish (dunno, can't ask her now, she's been dead a long time) - and according to anyone I can ask, ate everything willingly until perhaps 3 or 4 years old... and then it allllll changed and the range of foods I'd eat dropped dramatically.
I am dx AuDHD - my Dad is almost certainly AuDHD, my sister is dx ADHD - both display some food sensory issues but not to the extent of mine.
However... I am a super taster, neither of them are. I am fairly sure being a supertaster is likely to make matters worse for a kid with sensory issues/ND issues..
My own personal theory is that at the point kids realise that what they are given to eat may not be safe, instinctively, some kids respond normally to that, the range of foods they will happily eat without qualm drops... and then steadily goes back up again as they mature...
And those of us with a ND brain... don't do that.
But its hard to say as of course how parents respond has a huge effect - mine went down the force/abuse route, forcing me to eat things, hitting me if I gagged, same meal served up over and over until I ate it or it went off.. etc. So I don't know how much is ND brain and how much is abuse!