But I, like many others, CANNOT walk, cycle or use public transport, no matter how inviting the infrastructure or how much I dislike cars.
Not sure why you couldn't use multi-modal transport with a scooter and public transport? Not all public transport is accessible, but accessibility can and should be part of the focus of building/improving public transit.
Could I use a mobility scooter? Sure! But not in the cold and wet
I'm not sure why you couldn't use a mobility scooter in weather? I occasionally see some in Canada which are enclosed and temperature controlled. In the Netherlands, they have microcars which are an even better option for people with disabilities than a full-sized modified vehicle.
... and not when I can’t afford one.
Yet you can afford a car? Not only are mobility scooters usually cheaper than much bigger, more complex cars, but they are also subsidized (rightfully so) by medicare/health-plans.
Mobility scooters don’t fit in shops/cafes/restaurants unless they’re new buildings, which in the UK they’re invariably not.
Neither do full-sized vehicles/bikes/transit, so your point is moot. However, the smaller size of mobility scooters makes it easier to accommodate closer handicap parking than full-sized cars.
A small percentage of people will always need cars, just like we’ll always need ambulances.
Ironically, there's an argument that ambulances are public transit. They might be inefficient public transport, but they are an alternate to individuals driving dangerously to try and get medical help ASAP.
I think overall, your view of active transportation is really limited. Of course cars aren't going away but all your arguments seem to be limited by your experience of motonormativity.