What exactly defines a token character as a bad representation choice and not as a "background character" who happens to be disabled? And can a disabled character be the only disabled character but still good representation?
I know having relevant disabled characters is important, but when, besides the cast members who influence the plot, you have one of those scenes where a one-off character needs to be there, like when the autistic protagonist needs a ride in the middle of the road and a little person stops to help, or when the wheelchair user main character wants to talk to the magic council about a certain situation and the attendant is a blind person with a cane who checks the information of a braille book, is it safe from tokenism?
For this post I will use "representation" to imply good/decent representation, not just the act of XYZ minority technically appearing on the page.
There's definitely a lot to discuss when it comes to tokenism, and there are a lot of different criteria that you can use to define what exactly it is.
So I'm gonna start with the main definition of what would differentiate a "token" from an unimportant character (=one that doesn't influence the actual plot) who just happens to be disabled: how you go about the fact that they are in your book(/comic/etc.).
If you put in the description of your work that it's "disability rep!" because there's this one guy in a wheelchair in one scene, that's tokenism: using a minority to simply boost/promote something as "diverse". That's the most annoying occurrence of it, there's so much media that people recommend as "XYZ rep" and when you look into it, the "rep" is a side character that shows up in two episodes and has like a line of dialogue. Sad!
To use one of your examples, tokenism would be if you claimed that your work has "dwarfism representation" in it because of that one guy who helps the main character in one scene. It's... just not that. That doesn't mean it's bad; if every single background character who wasn't a cisHet white abled Christian man (etc.) was supposed to be deep and thought-provoking then no one would be writing them, because that's not what a background character is supposed to be.
But - you could commit a tokenism with a character even if they are just a background extra who shows up once. Tokenism often goes with the fact that the token character could be swapped out for a non-minority one and nothing would change, since the key here is that the author doesn't really care: it's all just to say "hey, I got XYZ in my book!".
So if you were to write a background character that you explicitly mention has disability X, but then they do something that a person with that disability wouldn't be able to do - that's probably a token (if not, it's still a badly made character). It's there to "represent" a group, but it doesn't make sense and there is no point so to speak because the author just doesn't care.
In that way, many disabled characters are just tokens - because the writer is writing an abled character, but keeps calling them disabled. When's the last time anyone has seen a character with albinism who was blind or low vision? What's up with all those deaf characters who read lips and speak orally so well that you literally forget they are even supposed to be deaf? Why is that "tragically unable to walk" character... walking for the entire duration of the book? They're just tokens done with no care nor research, it's all diversity points and quirky aesthetics. Everyone wants to be "inclusive", no one wants to actually have a disabled character who experiences disability.
Another thing with background characters is what role they serve. Most of them are fine - cashier has a skin condition, guy ordering a drink uses a speech generating device, mom of an annoying kid doesn't have a leg, cool. But sometimes it's worth to just ask "why am I making this specific character, whose disability has no impact on the story, disabled?". That is to say that if you need a prodigy piano player and your idea is to make them totally blind who always wears sunglasses, or to make the generic murderer have a big burn scar on half of their face, you're repeating a stereotype.
"Role" also encompasses what happens to them. Does the one disabled guy just... die, and that's all? That's a token.
Those are the main things I'd avoid when it comes to background characters. Don't claim that they are what they aren't or represent what they don't, and if you want a disabled character - even just an extra - then either commit or just don't do it, and keep in mind where you're putting them in the first place.
Can a disabled character be the only disabled character but still good representation?
They sure can, but they just aren't, usually at least. The problem with single character representation is that it puts a big burden on this one character: to represent a whole community. That's a lot. I've found myself in this exact spot before: small cast, one character is disabled, and I try to make the whole thing better and more authentic... every single time the result was adding more disabled characters, even if their roles were smaller. It's about the potential contrast.
There are choices that you can do when you have multiple characters of X minority that you should probably avoid if there's just one of them. If I see a work that has three blind characters and one of them wears sunglasses, my reaction will be "oh, cool, they have photophobia like me". If there's one blind character, and they wear sunglasses, my assumption will be that that's what just the writer thinks all blind people wear.
(Even though, that singular character could 100% also be photophobic. My assumption here is based on my experience, because that's how it usually goes.)
In that case you can find yourself in a place where you either need to subvert a bunch of stereotypes (some of which are based in fact!) or address it in one way or another in your work. That character could say "oh, I wear sunglasses indoors because even artificial light really hurts my eyes", but in order to do that, you need to be aware that this is a writing trope in the first place. Not to mention, if you do it too much, it starts reading as some sort of disability PSA. There's a fine line to everything, and the fewer characters of a particular minority you have, the harder it is to navigate it in a way that feels natural to actually read.
Sometimes the occurrence of just a single disabled character also raises some questions. Where's everybody else at? There are some exceptions to that (e.g. stories with a very limited character count) but generally speaking, everyone knows someone who's disabled in one way or another, especially if they're disabled themself. Books tend to make disabled people seem as a rare phenomenon, but that's really not the case.
Sometimes it borders on nonsensical worldbuilding - all those disabled characters who only get their mobility aids/meds because they Know A Guy (or are that guy)... I always ask myself, "what about all those people who don't know this one specific guy? what about everyone who lived before and after this one specific guy?", and I don't think the authors ever consider that. Unless the world population count is in triple digits at most, your character won't be the only disabled person. Writing in a way that subconsciously implies that they are is to me just another form of tokenism, because they're not only the only disabled character in the story, they're also presumably the only one in that universe overall.
This is just a lot of paragraphs to say that you probably aren't ever fully safe from tokenism unless there are multiple disabled characters who have at least somewhat important roles in the story - and even then, they can still be badly written, just in different ways.
Sorry for the long post but I hope this helps,
