It may evolve in the future, but currently, you must define the WEBVIEW2_USER_DATA_FOLDER environment variable manually as explained here WebView2 Globals, something like this:

public sealed partial class MainWindow : Window
{
    public MainWindow()
    {
        this.InitializeComponent();
        Environment.SetEnvironmentVariable("WEBVIEW2_USER_DATA_FOLDER", @"c:\temp\mydata");
        MyWebView.CoreWebView2Initialized += MyWebView_CoreWebView2Initialized;
    }

    private void MyWebView_CoreWebView2Initialized(WebView2 sender, CoreWebView2InitializedEventArgs args)
    {
        // udf will contain c:\temp\mydata
        var udf = sender.CoreWebView2.Environment.UserDataFolder;
    }
    ...
}