Cut objects in Gimp does not work?

I have a problem. I downloaded a PNG image from the Internet and wanted to cut an object and paste it into another image. I simply dragged the image into Gimp via the "Open" button. Then I went to this linen symbol. Then I carefully edged my object and made sure that there are no gaps between the beginning and the end. But when I right-clicked on the unwanted part of the picture, clicked on Invetieren and then went to delete, the whole picture plus my Outlined object has become transparent.

What can I do? I've tried it hundreds of times.

PS: The line of my rimmed object does not move, but there's a line around the whole picture that moves. Does that mean something?

Take a look at YouTube, then you'll find your mistake.

Since Gimp Version 2.10, a completed selection must be activated by double-clicking in the selection area or pressing the Enter key.
Until then, it can still be changed, but has no function.

After you have returned to the starting point with the "Leash" (you probably think the free-choice tool), press the Enter key once. The border of the selection then changes to a WWandering ants' line.

As already written: selection really finished?

Make a try first without having to release everything again.

Triangle with 3x click and 1x confirmation with Enter → then you have marked the area and you can use it for example. Cut out.