It’s a balance, to be honest.
Only way to test if someone is legally covered by the disability provisions in the Act is at Tribunal. Few employers want to do that, so they will err on the side of caution. Lots of things wouldn’t be reasonable in lots of circumstances, but I have seen requests for:
someone wanting us to modify ambulances so that they could bring their assistance dog (not sight related!) in the cab (refused)
a receptionist who wanted to wfh permanently (we agreed a move to a role that could be undertaken from home)
Someone who wanted to dictate who they would and wouldn’t work with, including managers (refused)
Generally speaking, changing hours, extra breaks, standing desks, allocated parking, fixed desks, changes to how managers interact (eg providing written notes and agendas up front), specific software for text to speech or speech to text are fairly easy to allow most of the time.
A close relative was non-public facing for an emergency service. They have a chronic condition that, amongst other things, means they can’t regulate their body temperature. Their employer refused to let them wear a heated body warmer under their uniform (so nobody would be any the wiser) until we threatened a disability discrimination claim. That was pretty ridiculous.
Employers don’t HAVE to agree them, but if a Tribunal ruled that something was refused that would be considered reasonable by a reasonable person, there are hefty financial risks.