I do not know about cloudflare's internals, but I believe the 6 connections limit is purely a browser thing. So it should be able to do as many connections as it's able to handle.
Ah okay thats good news. Is it worth upgrading to HTTP2 on the server side for cloudflare if they are the only consumers of my VPS? They already enable HTTP/3 for clients but I'm wondering if I'm somehow bottlenecking them by not matching my server with HTTP/2 or HTTP/3.
In general connections between CDNs/reverse proxies and origin servers don’t get much benefit from HTTP/2 or HTTP/3. CDNs don’t generally care about connection establishment speed or multiplexing to the origin (the main benefits of newer HTTP versions), since they can just create and maintain N long-lived connections if they want to be able to send N concurrent requests. They generally only bother with HTTP/2 to the origin if they need to support gRPC, which has some unusual connection semantics.