RSD is awful to live with, it was a key part in my social deficits criteria for my autism diagnosis.
Basically, it's a fight/flight/freeze/fawn response to the extreme when there is either valid or perceived criticism, so yes, the criticism can be valid, but it can also just be how I have interpreted the information being given to me, but my neurological response swings to immense and extreme distress, to the point I can get shouty, teary, scream, or just completely shut down.
Obviously not everybody knows what RSD is, or that I struggle with it and so it causes social rifts when I have these reactions.
To be honest with you, I didn't know this was RSD until I was almost 30.
When I could finally name the beast, it helped so much with managing it, because I could explain to the people around me that when they offer me criticism, before they expect a response I need to take time to pause and process the information they have given me, and put in place techniques I have learnt in order to prevent catastophising, and instead of focusing on the worst possible interpretation, I can start from the best possible interpretation and work my way back from there, but as this goes directly against the uncontrollable neurological distress it causes me, I will be quiet, withdrawn, and may even need to refer to my notebook to write down my thoughts before we can put any action in place.
This has meant small interactions like my family member picking up a spoon from the cutlery drawer that still has a bit of a smudge on it and saying "ugh, this one is still dirty" and me curling up, thinking I can never do anything right, and they just said that to get to me because they just want to get under my skin because they've always hated me and they just set me up to fail, to realising yeah that spoon has a smudge on it, it was wet, I thought I'd done a good enough job wiping it, but do you know what, I'm only human and how many times have I been to restaurants and been given a smudged spoon, realised that the person who put them in the wash was also human, and just gone back and got another one that didn't have a big smudge on it, and that I owe myself that same grace.
In the case of the OPs member of staff, if group, company wide emails, or community access data had bold and underlining on it, it probably wouldn't trigger me personally because I know it would be being sent to everybody, but if my direct line manager was sending emails specifically to me, and it had a lot of bold, capitals, and underlining then I would probably feel a little bit attacked. I don't think it's unreasonable where possible to ask that this is taken into consideration, but sometimes key elements do need highlighting in bold, or underlining, because I am also autistic, and find processing a lot of visual data at once to be overwhelming, and a big part is recognising that the text changes are for my benefit, and not for my detriment.
I had some OT sessions through the NHS where I brought up RSD, and my OT was wonderful about it, and wrote recommendations down, as well as advocacy service details if I ever get a job where I need mediation to discuss ways of working with my strengths and not against my weaknesses. I would only ask for my boss to consider these things, but I also would be able to forgive is they forgot about these things, because like me, they are human, they have a lot to manage, they are no more perfect than I am, and learning about people isn't linear.