Hi KevinChu7,
Thank you for reaching Microsoft Community. I understand that you're experiencing issues with your Surface Pro 7's display. Based on the information you've provided; it seems like the issue might be related to the display itself or the graphics driver.
Have you tried pressing the Windows key + CTRL + Shift + B to reinitialize the display driver of the device? If not yet, please do so then see how it goes.
If still issue persists, please try these steps while connected to the external monitor:
Open Device Manager
Expand Display adapters
Right-click on Intel(R) Iris(R) Plus Graphics
Select Uninstall device
Expand Monitor
See if the Surface Panel shows up, uninstall it also if yes
Restart the Surface then see how it goes
Additionally, please make sure also that all updates are installed including Optional updates in Windows Settings > Updates & Security. Check also for the Surface drivers' health through the Surface app then run the Surface Diagnostic Toolkit to run some system checks and repairs. See: Fix common Surface problems using the Surface app and Surface Diagnostic Toolkit - Microsoft Support
Let me know how it goes.
Kind regards,
Marrion