Hey,
We disabled Cloudflare caching months ago, so it’s not possible to use those headers as of today. If you really need caching, a workaround is described here: Koyeb CDN Ignores max-age Cache-Control headers.
Is Using Cache-Control and CDNs to Improve Performance and Reduce Latency - Koyeb the blog post you were reading? We will update it to make it clear this is not something we currently support.