Unassigned by IANA; in the wild it is VNC display :22.
5922 falls inside IANA's Unassigned 5915-5962 block, so nothing has a claim on it. The realistic listener is an RFB server on display :22, since VNC maps display :N onto 5900+N. The number is memorable enough that people also pick it by hand for a VNC session, the way 2222 gets picked for SSH.
Do not expose
Do not expose a VNC display directly. Tunnel it (ssh -L 5922:localhost:5922 TARGET) so authentication and confidentiality come from SSH rather than from RFB.
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