I have read TLS v1.3 RFC and haven't quite understood - does server certificate chain, that is sent to the client, MUST contain intermediate certificate or it is not a strict requirement (e.g. SHOULD or MAY)? I haven't found a reference for this question in the RFC.
The only info about that in RFC I found is:
The sender's certificate MUST come in the first CertificateEntry in the list. Each following certificate SHOULD directly certify the one immediately preceding it.
But SHOULD is not MUST!