No IANA assignment and no established convention; the port number tells you nothing.
IANA leaves 12265 unassigned, inside the same empty stretch between 12172 and 12300 that swallows most of the 12200s. Nmap's scan-derived list has it as unknown at a low rate. There is no public documentation of any application, appliance, or backdoor defaulting here. Anything you find is a service someone configured onto this number by hand or via a container port mapping.
Expose with care
The exposure verdict belongs to the service you identify, not to the number. Fingerprint it first.
$ nmap -Pn -sV -p 12265 TARGETSeen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.