Documentation for TAwait.ExecP<TModalResult>(newform.Execute);

[Debroy_Julio1 (Debroy Julio)]

I use the older method and it is working as expected now. I uploaded the test project with the solutions I found, here:

Error when destroying a form instance

Most efficient would be to start from our Multiform demo and modify this demo so the error shows and send this sample source project so we can investigate.