These are the limitations mentioned on the docs [1]. Quick Tunnels are subject to a hard limit on the number of concurrent requests that can be proxied at any point in time. Currently, this limit is 200 in-flight requests. If a Quick Tunnel hits this limit, the HTTP response will return a 429 status code. Quick Tunnels do not support Server-Sent Events (SSE).

[1]: https://developers.cloudflare.com/cloudflare-one/networks/co...

I don't know if there's an overall limit, but their regular tunnels have a limit of 100 MB per request which breaks stuff like Immich.