according to this: https://news.ycombinator.com/item?id=10819711 over 94% of websites do not use a reverse proxy at all.

Of those, 70% are using cloudflare as their reverse proxy... so 4.2% of websites use cloudflare.

This page: https://www.datanyze.com/market-share/dns/ says 70,000 of the top 1M websites use cloudflare DNS

I've seen other sources quote cloudflare at 2-4% of websites using them as their CDN.