Hi JosonJames,
My name is Merlina, I am an Independent Advisor. I'm Sorry to know that you're having this issue. I'll do my best to help you.
Try these steps to troubleshoot the issue with the display not adjusting to system's night mode in Windows 11:
If you have any third-party software installed that controls the display color temperature, try disabling it and see if that fixes the issue.
Step 1: Check your display settings.
>Press Windows + I
>Click on System.
>Click on Display.
>Under the Night light, make sure that the On switch is turned on.
>Use the Strength slider to adjust the strength of Night Light.
Step 2: Update your display driver.
> Press Windows + X
> Click Device Manager
>Expand the Display adapters category.
>Right-click on your display adapter and select Update driver software.
>Click on Search automatically for updated driver software.
>If the issue persists, right-click it then uninstall, then restart your PC then check.
Step 3: Reset display settings
Go to Settings > System > Display > Advanced display settings > Display adapter properties for your display. Then, click on the "Monitor" tab and click on "Properties". From there, click on "Driver" and then "Roll Back Driver" to reset the display settings.
Let me know the result. Thank you!