There is no definitive list of disabilities to the best of our knowledge, although it’s often presumed that there is. It’s similar to the way people often believe a disabled person is ‘registered disabled,’ which they aren’t.
The DWP used to use a handbook of the 50 conditions which would qualify for consideration of a disability benefit award. This ended 10 or so years ago.
You are regarded as disabled under the Equality Act 2010 if you have a physical or mental impairment that has a ‘substantial’ and ‘long-term’ negative effect on your ability to do normal daily activities.
By ‘substantial’ they mean it takes much longer than it usually would to complete a daily task like getting dressed. By ‘long-term’ they mean 12 months or more, like a breathing condition which developed as a result of a lung infection, for example.
Then there are special rules about recurring or fluctuating conditions such as arthritis. It’s a bit of a minefield to be honest!