I use Firefox Focus on my mobile and I can’t enter sites with CloudFlare because it says my browser is incompatible.
I also use Firefox Focus and I never experienced that issue at all. Are you sure this is a Cloudflare issue?
Also, site owners are purposely using Cloudflare to protect themselves from abnormal traffic. If site owners are the ones paying Cloudflare to lift these barriers, why do you interpret this issue as a problem created by Cloudflare?