If you use Rakuten Cash Back with Kobo (aka Walmart eBooks), it looks as if the discount for e-books (which I guess count as “all other items”) is up to 10% right now. I haven’t personally tried it yet, though. See this screenshot from this morning (Sept 20, 2021):
I don’t think Rakuten varies the percentage by individual user, but not totally sure of this, so YMMV…