The display will flash

The display will flash if one output port plug in or out.
For example: if hdmi port plug out, dp port connected screen will flash a time.
Is the phenomenon normal?

That will trigger some handling at the display frame buffer reslution change for output.
Same behavior can be observed at PC/laptop while plug in and plug out an external monitor, that’s normal.

Yes, we also found at PC,but our PC all are hdmi ports, but, we have a query: Nvidia device board is one hdmi ,one dp port, I think different port types shouldn’t affect each other.

If you try with laptop then can see it, the plug in-out trigger some activites to display driver to handling the resolution and framebuffer changes.

For perspective, consider that the DP or HDMI is just the PHY, and this is then abstracted to the GPU itself. The GPU isn’t really aware of the type of connector, and both provide configuration information (partially in the form of detection that the port is present or not, and partially in the form of configuration data, the EDID).

Some part of the GPU has to have a driver reaction to losing about half of the video data output destination. If computing power is not using half of the GPU now, then I suppose you could avoid a reaction if the elements of the GPU were to remain static and the unused parts of the GPU were to remain lost.