Hi Rose, I am in Canberra too and finished radiotherapy in January. I had chemo before that and took six months off work. I started back on Friday four days a week. I used to work really long hours due to there being a lot of administrative work on top of my main job but will not be doing that any more as it was not really appreciated or recognised and I have realised that I need to put myself first from now on, and have a better work life balance. I personally don't seem to have brain fog, but its only early days. I had a very good memory before and so time will tell if it feels like my memory has suffered. I've worked in the same role for seven years so I am very across it, which probably helps - although when returning to work I did feel like it is mostly the same and that it would be nice to do something different that is a bit more challenging, while also not requiring really long hours. I am going to keep an eye on the jobs that are advertised in my field for the next couple of months, and hope something suitable comes up.
My boss has been supportive of me returning four days a week. I hope your discussions with your boss and HR are productive.