Okay, this is really long and still only a jumping-off point but I am hoping it provides a perspective and a decent overview of wheelchair accessibility options/issues for an Airbnb.
Wheelchairs and Entrances:
There is actually quite a lot of grey area here. In fact, most of it is grey area. The ADA requirements are quite generous as they are meant to accommodate the almost-everyone of the public and they only apply to businesses/public areas, not residential housing. It would still be extremely rare for residential spaces to be ADA compliant. It is actually very unfortunate, and not particularly helpful, that Airbnb is using ADA standards for their Accessibility section. It seems you can only say that it meets ADA standards or that it doesn’t. It would be most helpful if each listing could say yes or no and then show their entrance and make notes, show their doorways and note the measurements, etc. This would even be helpful to people who need something more than ADA minimums. But, it is what it is, so just ranting 
What I am saying is that your home can be accessible for a lot of people without being ADA compliant. Other than people who live in some kind of facility or specialized housing, most people who use wheelchairs live in regular homes like ours, particularly as far as doorways go. Most wheelchairs will fit through a 30 in doorway, many will fit through smaller doorways. Most people in wheelchairs know what width of doorway they need. If they don’t know (usually the elderly who have recently started using a wheelchair), they can find out by measuring the doorways they are successfully accessing at home.
One reason for this is that the ADA standard of 32” is to allow a person to independently access the doorway, so it includes room for their arms/elbows while propelling as well as any needed slight angle (e.g. not a straight on entry, like a bathroom off a hallway). So, obviously, if the person has someone with them (which is common for traveling), the wheelchair can be pushed through a much smaller doorway by the 2nd person (while the person in the wheelchair keeps their arms in).
The other reason for this is that the most common wheelchair is actually, on average, an 18” seat, which actually only needs a 27” doorway. The common W/C size can obviously vary, e.g. bigger people need bigger chairs. Some adults use chairs as small as 14” seat (which fits through a 23” doorway); however, there are people in 22” and even 24” chairs but I am confident that these don’t likely make up much of the traveling public (you’ll have to trust me on this ,)
The other element is that there are different types of wheelchair users. You may be able to accommodate some W/C users but not others and that will mostly have to do with the other accessibility features you can offer and whether or not they are traveling alone:
There are people who only need the wheelchair only for distance, because of respiratory/endurance/coordination issues and have no trouble navigating short distances inside a home (e.g. from the doorway to the bed or toilet). These folks can also navigate a couple of stairs at the entrance (but a flight of stairs wouldn’t work). Sometimes they use a walker/cane/crutches inside the home (as @jaquo mentioned), or not. They are likely traveling with others. They will need to sit down for showering/bathing. If your shower stall has a seat in it or if you are willing to provide a removable seat for your shower or tub and there is at least one grab bar, you could accommodate these folks with any size doorways as long as you have no more than about 3-steps to enter (and a handrail for some).
There are young, spry, athletic users who are in ‘sporty chairs’ which are very lightweight and small-framed and low to the ground. These are generally people with spinal cord injuries who use these chairs like legs and are very independent. They know exactly what measurements and access they need (and it will be much less than you think). A step or two to enter (even more for some) won’t get in their way at all. They “wheelie” up steps and over curbs routinely. They also go down steps in their chairs just fine. Many play sports in their W/Cs. They travel and they travel alone and independently. You can usually accommodate this type of W/C traveler with 27” doorways (for the rare one that needs more, they will know and not book as long as you can give them the correct information), depending on the layout of the rooms. They will need grab bars at the toilet and in the shower and will require grab bars and a seat for the shower. A low or average height bed will be preferable. If they are arriving by car, they will need a parking space where one door can be opened all of the way - on the street is okay. A floor plan of your space will help these folks a ton.
There are people who are in W/C because they no longer walk (or don’t walk safely). This might be who we generally think of when we think of W/C users - gramps after a stroke, auntie with an awful disease, etc. This is a big varied grab-bag of wheelchair users and they may be traveling but will be traveling with others. Since they are traveling with others, the others can push their W/C through the doorways for them - so they don’t need 32” because they don’t need to self-propel through the doorway. Many of these users are not self-propelling anyway and may even be in a “companion chair” or “transport chair” (as @momovich mentioned) which has a smaller width and no way to self-propel (no big wheels on the side) anyway. Even people who use a wider chair at home often travel in these smaller chairs that require being pushed. These small companion/transport chairs fit through any doorway that is not in a hobbit house. However, this group of travelers will require grab bars at the toilet and the shower and a place to sit in the shower. They will need an average height bed (not on the ground and not princess-high). If your doorways are under 30”, you can accommodate many of these folks by providing a companion/transport chair inside the home. These can be bought used at Salvation Army, garage sales, etc and can be found sometimes for free from churches, elder councils, etc. These folks do require a flat, very low or ramped entry into the home. Steps are a deal-breaker for these users with the exception of a low 1/2 step at the entry. Their companion can safely and routinely get the W/C over a bit of a raised entry (but less than a full step).
And then there are people with severe disabilities in very complex specialized wheelchairs. They usually have a tilt and a recline and leg rests and head rests and other extensive accessories on their wheelchair. They need a lot of room to turn around and to move in the space. It is highly unlikely that you can accommodate these folks in your home as they will need the full ADA minimums and don’t have the option of being in a different type of chair. If they are using Airbnb they are only looking for places that are fully ADA compliant.
TL; DR: If you’d like to be more accommodating of people who use wheelchairs, it is unlikely your home will meet ADA compliance as homes are not subject to the ADA so most homes don’t; however, there are options. It may be as simple as some grab bars, a floor plan with basic measurements, a shower seat and a little bit of extra communication. And don’t forget you can sometimes gain several inches in a doorway by changing hardware or reversing the swing (or replacing with a sliding barn door type door if you’re up for it). Airbnb’s system does not really support us in truly being accommodating as their listing tools only allow for ADA full compliance or not but if you’re able and willing to do a few other things it might be worth noting in your listing that you are interested in being accommodating and can provide a floor plan and/or measurement information/pictures and definitely tick-off the accessibility features you do meet (e.g. well lit entrance, grab bars, shower head, etc).
is a great example. When I thought about having an Airbnb my ideal was to really deck it out and make it ultra-accessible. I was dreaming big: transfer-lifts and all! I pictured quad-rugby teams mapping my place out for their next road games, hospitals with my card on the discharge desk, droves of dependent grandmas joining their families for vacation again!
And even if I invested in an exterior mechanical lift to get people up the 7 stairs to the first floor, the inside of the house is a minefield of safety issues for most disabilities. So, I have hand-held shower heads but I don’t tick the box under “Accessibility Features” because I don’t want anyone to think that my house is Accessible just because they see “Accessiblity Features” pop-up. It could be a really bad situation for a guest who doesn’t read the whole thing, so I leave it out.
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