My advice is to earnestly try your best without compromising your health or mental health, and then mercilessly advertise doing so. What I mean by that is, try

My advice is to earnestly try your best without compromising your health or mental health, and then mercilessly advertise doing so. What I mean by that is, try to peek at emails/chat when you can, and send a message. Let folks know when you're having a rough day but ALSO when you're going to power through and show up to a meeting. Try to do a good job and go overboard on advertising you are working to make up the times you can't be around due to your medical treatments. You want people to root for you, both for your health, and for your success at the company. Sometimes it doesn't take much for a boss to recognize "oh, they're trying to do a little extra".