Authenticating using ConfidentialClient

.NET 認証に関するこの質問が msgraph-sdk-java リポジトリに属するかどうかをまず確認し、その後、報告されている GetAppAuthentication 関数と ConfidentialClientApplicationBuilder の利用可能性リンクを確認します。Windows Service および WinForms のシナリオでこのエラーが発生する理由を特定し、サポートされているアプローチを文書化または確認できれば完了です。プロジェクト ファイルやテストは指定されていません。

Hello,
Some of our customers are unable to send out automated emails because support for basic authentication with SMTP is being removed.
I am looking at finding a solution and it seems the Graph API is the recommended approach.
I have manage to create a working example using PublicClientApplicationBuilder however, this class displays a pop-up requiring the user to sign in, since we have automated services with no user interaction, this is not a good solution.
I have seen some examples using ConfidentialClientApplicationBuilder and this seems idea.
However, I have reached multiple dead-ends and everytime receive the error:

Confidential Client flows are not available on mobile platforms or on Mac.See https://aka.ms/msal-net-confidential-availability for details.

I understand that it is limeted by design (see issues/742) but ConfidentialClientApplicationBuilder throws this issue for every project type I try, WinForm, Windows Service, Console app.
I have got it working on a ASP controller but they is not practicable for our customer.
I am storing my Client, Tenant and Secret in a database table and here is my code:

Private Async Function GetAppAuthentication() As Task(Of AuthenticationResult)
    Dim folderAccess = BLL.L2S.SystemApplicationGateway.GetFolderAccess(mBLL_SY.ReadonlyDbContext)
    If folderAccess Is Nothing Then
        Return Nothing
    End If

    Dim app = ConfidentialClientApplicationBuilder.Create(folderAccess.Client) _
        .WithClientSecret(folderAccess.Secret) _
        .WithTenantId(folderAccess.Tenant) _
        .Build()

    Dim scopes As String() = {"https://outlook.office365.com/.default"}

    Dim result As AuthenticationResult = Await app.AcquireTokenForClient(scopes).ExecuteAsync()

    Return result
End Function

I am using .Net Framework 4.7.2, we have Windows Services and WinForms apps and both need to send out emails.
The error message is very confusing to me because of course it is not a mobile app, and I have even created a UnitTest that seemingly works fine which again is very confusing to me.

This is urgent as this is already causing issues for our customers.

Thanks in advance.