Displayport is working at boot process and stop working after entering the system (iGPU with both HDMI and DP)

OS: MacOS Big Sur (OpenCore)

CPU: i7-9850H

It's a mini PC (NUC alike).

Hi, my mini PC has two display ports, HDMI and DisplayPort. Both are working in Windows and Linux. I can use two monitors together in Windows and Linux.

But with OpenCore MacOS Big Sur, my DisplayPort has a problem. HDMI is working fine.

Regardless whether the HDMI cable is connected to a monitor or not, when I connect the DisplayPort to a monitor and start booting MacOS, I can see opencore boot menu in DP monitor and I can see the booting process (many texts output in the screen). Since I am using FileVaule (APFS encrypted), I can even see the Password Prompt GUI screen in the DP monitor. After entering the password and Enter, I can continue to see the booting process (many texts).

But as long as the booting process is completed and entering the system, the DP monitor will stop working and lost signal. This happens when I connect the DP cable only AND when I connect both HDMI cable and DP cable to two monitors.

When I connect to one monitor, I can not do anything other than a reboot. Because I can not see anything.

When I connect to two monitors, the HDMI screen will show the MacOS system fine. In the System Preferences > Display, it can only detect one monitor (can not detect the DP monitor).

PS: when I connect with two monitors, both HDMI and DP monitors can see booting process fine at the same time.

Can anyone help me on this issue?

I checked the BIOS, I don't find anything I can change to fix such problem. The CSM setup is disabled in BIOS. I found somebody online mentioned that turning off CSM will fix DP issue, but mine is off already.

Thank you very much.