And just another question. The effect of “xrandr” may only take one time. Which means if you reboot the device, then previous error shall happen again. Does this happen to you or not?
The system was initially setup via HDMI cable. This case was working fine.
After a month I changed HDMI to DP and the system didn’t recognize it automatically, so DP was unavailable until I run the command.
After reboot DP is still working.
Probably, If DP were be the first connected cable then the system automatically setup it.