This pattern — display goes fully black under load/heat but audio and keyboard backlight stay alive, then recovers after an hour of cooling — points pretty specifically at a hardware issue rather than anything software-fixable, and you've already ruled out the usual driver/OS culprits.
Next time the internal screen goes black, connect the laptop to an external monitor via USB-C. If the external display shows an image while the internal panel stays black, this confirms the GPU/display controller is still processing video — the fault is in the internal display path (panel, connector, or the controller's connection to it), not a total GPU failure.
The most important clue here is that the computer itself remains powered on while only the display fails, and cooling temporarily restores it. That makes a temperature-sensitive hardware fault worth investigating.
Since you bought this used, you won't have original AHS/manufacturer warranty coverage, but Microsoft does offer paid out-of-warranty service for Surface devices.