As long as it's not an "on demand" business like a hands on shop, cafe, garage, hairdressers, etc., I think it's quite possible, and common, for people with chronic conditions to be self employed.
So, basically, all kinds of "consultancy" or professional businesses, or cottage industries (art, crafts, pottery making, etc)., where things need to be done, but not necessarily immediately, and could be planned in within a few days or a week or two.
One of my clients is a potter with a wheel/kiln etc in a garden workshop and she's got treatable (by long term chemo), but incurable cancer, so just makes her pottery around the days when she's not having chemo and feeling well enough to do it. During chemo sessions or otherwise when she's not well due to the chemo and it's side effects, she doesn't go into the workshop, so it's often a pattern of 3 weeks working and 1 week off, or 2 weeks on, 2 weeks off.
Another client runs a virtual office business, doing website domains, email hosting, mail forwarding, registered office addresses, etc., which is basically all contracted out to other firms - he just does the marketing and administration via websites, social media, etc., and takes commissions and affiliate commissions from his web sites, website directory entries, tik-tok/facebook/youtube ads/links, etc. So, again, he just "works" when he's feeling up to it, but 99% of his business is automatic, so he can just ignore it when he's not up to it. He's in a wheelchair and has very restricted bodily movement/functions, but his brain is 100%, so he uses his brain rather than his body, hence the writing of websites etc and moving into social media influencing.
So it does depend on the type of business and the effects of the medical condition. I think people with chronic conditions are probably better being self employed so at least they have control over their work, clients, etc., whereas it must be a lot harder when employed by someone else.