How so? Cloudflare R2 targets B2, but technically you're not supposed to use Cloudflare for free B2 egress unless you are on a paid plan.
https://www.cloudflare.com/bandwidth-alliance/backblaze/
Maybe you're referring to the "Limitation on Serving Non-HTML Content"?
https://www.cloudflare.com/terms/#28-limitation-on-serving-n...