In the meantime, in the age of Covid, I've been rereading a bunch of my nonfiction writing books. (How about you?) Writing advice really differs. At least one nonfiction author recommends keeping a writing journal and writing in it free hand everyday to keep the creative juices flowing. Another says keep a notebook/note app with you twenty-four seven to jot down ideas (like Agatha Christie!). One says write down ideas on a big sheet and connect them in a kind of idea cloud.
One says reject your first ideas because they're too obvious.
There's also the old adage: Write what you know.
I've been ruminating on all this advice. I think you should write what you're passionate about. When you write what you care out, the story comes alive for the author. This makes it come alive for the reader.
Bottom line: do whatever works for you.
Good luck whatever you decide to write about!