BC survivor here. First and importantly, wishing you all the best and sending a big virtual hug. I hope you are navigating everything as well as possible. I went to WDW in the middle of my treatment, and it injected such joy into a scary and trying time. I hope it does the same for you.
There is the dessert party with seats (not the best projection views, but you can see them), but in my experience, you have to get there a bit early to get the best seating. If that doesn’t appeal or isn’t in the cards, Tomorrowland is a good option, as is Fantasyland - either behind the castle (more people, but there is seating) or near the Little Mermaid area (usually empty). Another option is watching from a resort - I think the Grand Floridian marina area is especially nice and uncrowded, even though it’s off center. Poly is more centered, but attracts more people.