Let’s be clear here. Cloudflare isn’t a CDN. They call a feature of their service Cloudflare CDN, but at a fundamental level that’s not what it does.
The two elements which usually intersect with Discourse are their DNS (fine, good even) and their reverse proxy - the orange cloud while using their DNS product.
The reverse proxy can cache uploads (which is ok) but can also interfere with the javascript payload delivered to the browser (typically not ok, and the element we’re discussing here). As a reverse proxy it also increases latency for all communication between client and server, which directly impacts user experience.
Cloudflare tunnel is mentioned elsewhere on meta and is fine for the application where it’s highlighted.