How to copy a temporary edit image with changes to another application?

[rich2005]

That checker pattern is transparency, the alpha chanel

Before anything else, turn that off. Layer -> Transparency -> Remove Alpha Channel

Now you can make the selection and Edit -> Cut
next Select -> None and Edit -> Copy before pasting...where you want to paste.

If you can get see this, 30 second animation: https://i.imgur.com/azBtnCx.mp4