Other software is always a user option. This basically the previous advice.
Round shape - remove plain background:
Add transparency - Layer -> Transparency -> Add Alpha Channel
Select the background with the fuzzy select tool.
Grow the selection one or two pixels - Select -> Grow
Cut the selection.
Copy that: Edit -> Copy
Paste that into another canvas
Edit -> Paste As -> Paste As Single Layer
Move that layer into position with the Move tool.
...and as a one minute video (no audio) https://sendvid.com/9r66a6r8
Round shape - remove plain background:
Add transparency - Layer -> Transparency -> Add Alpha Channel
Select the background with the fuzzy select tool.
Grow the selection one or two pixels - Select -> Grow
Cut the selection.
Copy that: Edit -> Copy
Paste that into another canvas
Edit -> Paste As -> Paste As Single Layer
Move that layer into position with the Move tool.
...and as a one minute video (no audio) https://sendvid.com/9r66a6r8