Does Facetime use QUIC ?

because on the internet I have not found anywhere the possibility that QUIC can be used other than ports 80 and 443?

QUIC is a transport protocol, akin to TCP or UDP [1]. It’s perfectly fine to run it over any port, assuming that both peers agree on the port to use.

HTTP/3 is HTTP running over QUIC, in the same way that HTTP/1 and HTTP/2 are HTTP running over TCP. It usually targets port 443 [2] but, again, there’s nothing to stop you from using a different port number as long as both peers agree.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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[1] Of course QUIC is actually implement on top of UDP, so it shares its port ‘space’ with UDP, but that doesn’t change this story.

[2] Most HTTP/3 is HTTPS over QUIC. Indeed, that’s the only model that Apple platforms support. However, HTTP/3 does allow for insecure HTTP over QUIC.