Extremely variable how well supported students are. Some unis have excellent support processes in place, others are very bad at following them, some don't do more than just make vague gestures towards their obligations under the equality act.
Generally in my experience the issues are not with academics who have no issues with students who have reasonable adjustments due to a disability (although note usually you do need to have a formal diagnosis in order to be able to apply for Disabled Student's Allowance and have a needs assessment at your uni in my experience?). In fact they are often very keen to support such students from what I have seen.
The challenges, from my experience, lie within the accessibility departments at the universities themselves. I have had the experience where a uni provided very little support to me until after I had a formal diagnosis and was in receipt of disabled student's allowance (hence my comment about this above), and then once I had that gave me a needs assessment, discussed all kinds of wonderful things to help support me, then didn't put in place 90% of those and left me to just kind of fend for myself and try and keep chasing them up for the stuff. Equally though I've been at a uni where I've gone to them, had my needs assessment, and they put everything in place for me, were very quick to followup on any queries or concerns I had, and were active in reaching out to me to make sure that my reasonable adjustments were in place, were helping, if I needed anything changing with them etc.
So yeah, really variable but the issues aren't where you think they are, in my experience. Note though in basically all cases I've experienced, it's up to the student to make the first moves to apply to DSA from SFE, reach out to the relevant team within the uni, and get the process started. If you don't then they don't generally reach out to you (even if you are in receipt of DSA) in my experience.