You can just add a reference to the Windows COM objects that implement UIA:

Or just copy paste these COMReference XML elements into your .csproj:

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <OutputType>Exe</OutputType>
        <TargetFramework>net9.0</TargetFramework>
        <Nullable>enable</Nullable>
    </PropertyGroup>

    <ItemGroup>
        <COMReference Include="UIAutomationClient">
            <WrapperTool>tlbimp</WrapperTool>
            <VersionMinor>0</VersionMinor>
            <VersionMajor>1</VersionMajor>
            <Guid>944de083-8fb8-45cf-bcb7-c477acb2f897</Guid>
            <Lcid>0</Lcid>
            <Isolated>false</Isolated>
            <EmbedInteropTypes>false</EmbedInteropTypes>
        </COMReference>
        <COMReference Include="UIA">
            <WrapperTool>tlbimp</WrapperTool>
            <VersionMinor>0</VersionMinor>
            <VersionMajor>1</VersionMajor>
            <Guid>930299ce-9965-4dec-b0f4-a54848d4b667</Guid>
            <Lcid>0</Lcid>
            <Isolated>false</Isolated>
            <EmbedInteropTypes>false</EmbedInteropTypes>
        </COMReference>
    </ItemGroup>

</Project>

Note you might want to set EmbedInteropTypes to false depending on warnings you may face during coding.

And then you'll be able to use it simply like this:

using UIAutomationClient; // use this namespace to start

namespace UIAOpenTray;

internal class Program
{
    static void Main(string[] args)
    {
        var automation = new CUIAutomation8();
    }
}

PS: there's no need to reference WPF, but this is a bit different than using the System.Windows.Automation namespace, although very similar.