Reasonable adjustments denied for my ADHD

I was diagnosed with ADHD combined type last August, 40f, and started medication in February, which has been incredible, except for realising that in addition to this, I'm probably autudtic to, which makes so much sense. I told my manager about my diagnosis but never asked for anything until now.

I had a bad day in the office last week. Open plan office, my desk right above a fan vent that I have no control over, loud music blaring from Spotify on Bluetooth speakers in ceiling tiles, very very loud people, sat between two loud teams, no inside voices at all.

I emailed my manager, who was working from home and asked to go sit in another room for an hour or so so I could get a task done. She said no because somebody had to "be there" for other two junior members of the team, so I had to stay.

I ended up sending her an email, documenting how I felt, tried to explain overstimulation, where I was tbh too accommodating, trampling on my needs. Said I felt like I was doing a good job and wanted to continue but sometimes need quieter time in the month (work in finance so always on the monthly carousel of endless tasks).

She said she didn't want to reply by email (a red 🚩?) and would pick up with me on Monday, when she was back in. I ended up in A&E on Friday, had a severe UTI, which kind of explains the bad day

So we spoke on Monday once everybody had gone. I got "everybody feels this way at one time" and "we all struggle with the radio", to "I can't be seen to be giving you special treatment", "you can't work from home", "if you aren't at your desk, it will look strange", and the tone of "I can't be seen to be giving you preferential treatment over everybody else".

And like the idea I am, I again was too accommodating to her, said I understood her point but I need that time, so the answer was basically no, stay in this open plan hell that we all hate, just go away from your desk at lunch and that will pretty much sort it.

Then I realised that her relative works in a team nearby, has some physical limitations due to cancer and she works from home 4 days a week, and that's okay because she has a physical disability and mine is in my head, but really everybody has a bit of ADHD from time to time, right?

It's a small company, HR is there to protect management from staff, two friends have reminded me about reasonable adjustments but manager thinks I just crack on as I have.

If I raise an issue, it's going to get difficult and I'm not sure if I have the fight. I'm in burnout and I don't know how to make her understand what I'm experiencing.

Any help would be gratefully appreciated.