Sets the Windows 11 theme between Dark and Light.

Set-WindowsTheme.ps1

function Set-WindowsTheme {
    param (
        [ValidateSet("light","dark")]
        [Parameter(Mandatory=$true)]
        [string] $Mode
    )

    if ('dark' -eq $Mode) {
        Set-ItemProperty -Path HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize -Name AppsUseLightTheme -Value 0 -Type Dword -Force
        Set-ItemProperty -Path HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize -Name SystemUsesLightTheme -Value 0 -Type Dword -Force

    } elseif ('light' -eq $Mode) {
        Set-ItemProperty -Path HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize -Name AppsUseLightTheme -Value 1 -Type Dword -Force
        Set-ItemProperty -Path HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize -Name SystemUsesLightTheme -Value 1 -Type Dword -Force
    }   
    <#
    .SYNOPSIS
        Sets the Windows 11 System Theme
    .DESCRIPTION
        Sets the Windows 11 System Them to either Dark or Light.
    .EXAMPLE
        PS C:\> Set-WindowsTheme -Mode light
        Sets the Windows 11 Theme to light mode.
    .EXAMPLE
        PS C:\> Set-WindowsTheme -Mode dark
        Sets the Windows 11 Theme to dark mode.
    .INPUTS
        System.String. The mode of either light or dark that the system theme should be set to.
    .OUTPUTS
        None
    .NOTES
        Written by Matthew Johnson (@mwjcomputing)
    .LINK
        https://mwjcomputing.com
    .LINK
        https://gist.github.com/mwjcomputing/114042f37089208b5c562705fe966fec
    #>
}