title: Can't add custom ActiveX control to .NET Core WinForms app., but .NET Framework app works fine
body: <p>We make a C++ ActiveX control for years now. It's now built using VS 2019.<br />
  When I create a new .NET Framework v4.8 WinForms project I can add my ActiveX control to the toolbox in VS2019 and drop it on my form.</p>
  <p>But when I create a new .NET 5 WinForms project using VS2019 or a new .NET 6 WinForms project using VS2022 I can look up the ActiveX control when using <code>Choose Items ..</code> but when I select the control I get this error:</p>
  <pre><code>The following controls were successfully added to the toolbox but are not enabled in the active designer
  
  Make sure the controls to add are compatible with the current designer and .NET Framework version
  </code></pre>
  <p>I can however create the control using code in the designer and at run-time, the application works as expected. I can't open the form in design time, that will generate an error.</p>
  <p>Most likely I need to update my ActiveX control to make it more compatible with .NET Core, but I can't find what.</p>
  <p>Can anybody offer advice?</p>