What many people dont often do is create their own spells. It takes a lot of time and effort to come up with, and not completely break the game balance. But its really a wonderful part of the game when done within the context of "dont be an asshole gamer"

Creating unique elements for your characters/campaigns is some of the more rewarding experiences ive had with ttrpg.

That being said im too lazy and have generally just played hack n slash/murder hobo type games

But only mostly.

The best gaming experiences ive found are the ones where creativity is rewarded without disrespecting the table and overall group. When you have players collaborating over some idea they think is really good or just exciting to them. If its really dumb and stupid its probably going to be very satisfying when the dm controls the consequences well(even the negative ones!)

Failure should always be made to be simply a different path not a roadblock(sometimes that does mean rolling new character or whole party!)

It depends on the disability, the magic, and the DM's interpretation, I suppose. Lesser restoration is kind of a cure-all, gets rid of disease, poison, blindness, deafness, and paralysis, and 'disease' in particular might cover a pretty wide swath. Greater restoration can end effects that reduce ability scores or hit point maximums, which might include chronic conditions or congenital birth defects not directly linked to a disease. Regeneration can grow back missing body parts. Anything that these spells don't cover, Wish (and Divine Intervention) almost certainly would, but you'd be hard-pressed to find someone who could and would cast it.

No spell explicitly says it, but I kinda feel like Regeneration might resolve that concern. It's the go-to in the DMG for missing eyes and limbs. General high level healing (6+) will resolve scars, which one can argue that they should also resolve born stuff like epilepsy and the like since those are (kinda) lasting injuries akin to scars. Beyond that a case can definitely be made for Resurrection and it's ability to restore missing body parts. Feel like bringing someone back to life is a big step beyond just curing their paraplegia. Heck, there's an argument for Greater Restoration as well considering it resolves anything that lowers max HP or ability scores. Ultimately those are up to DM ruling but I doubt most would say no.

Then of course there's just straight up Wish but that's a whole nother thing.

Typically no as far as my understanding, at least not without some serious magic like a true polymorph spell (a 9th level spell)

Of course then you have the difficulty of finding someone who not only knows the spell but is willing to use it on some random person

Depends on the nature of the disability I would say.

A neurological disorder of some sort or some other difference would likely not be curable but some sort of magical item could assist, rather than completely 'fix' the issue. It would be kind of fun to see how a high charisma character with autism handles things though.

Mobility issues could be routed around with enchantments and such or the use of some kind of frame or wheelchair even. Something fancy or something crudely constructed.