Linux Mint on an Optiplex 780: No DP output?

I have Linux Mint 21.3 on a resuscitated Opti 780 (Core Duo, 2 GB RAM). I am getting satisfactory VGA output, but there is no output on the DisplayPort socket. Running the command xrandr to examine the video settings, I see a line stating "DP1 disconnected".

Is this a hardware issue or a Linux issue? If the latter, can anyone suggest a suitable Linux distro where the DP socket is active out-of-the-box? I am by no means married to Mint and welcome any suggestions.