There are several types of disabilities, the number depends on how they are categorized. One person might have more than one type of disability. And an important reminder is that having a disability does not necessarily mean any type of issues in cognitive function.
When I ask a group of people to think about what a person with disabilities might look like, I'm pretty sure at least one would imagine a person in a wheelchair. And another would probably imagine a blind person with a white cane. The answers people give usually tell me something about their experiences. Some might have a lot more people with disabilities in their lives than others.
While some of the disabilities can be identified visually, not nearly all can. There's really no way of knowing if the person next to you has a disability or not. Not that you'd need to know that either, but just to bring the point of invisibility across.
There are so many horror stories online of people getting harassed for, for example, "stealing" an accessible parking spot just because the accuser can't see anything "wrong" with the person. I really hope that with awareness we can reduce the amount of harassment people get for things like these.
And it's also good to keep in mind that not all people who have a disability want to disclose that to others, especially people they don't know. There is unfortunately still a lot of stigmatizing happening. So be mindful when talking about disabilities, especially if you talk about someone who has trusted that information with you and not necessarily with other people. Also, not all people consider themselves to have a disability even if they experience such functional limitations.
I also found it interesting that not all people with disabilities even realize they have a disability. But when you start to think about this, it does make sense. For example, someone with color blindness might not even realize they don't see all colors if that has never come up in some way. Unfortunately, this might mean, for example, that they aren't aware of any assistive technologies or other tools that could benefit them. I have heard more than once from a participant after accessibility training that they had never realized that accessibility also applies to them. So there is a lot more awareness needed for this topic for all of us. The more we understand, the easier it is for us to create more accessible products and environments for all people.