If you want to save your image without a background colour to use as a sticker or overlay or similar, then follow these steps:
Open the File Menu and select Drawing Settings (this might only be possible if you are the owner or admin on the canvas);
Set the background colour to Transparent and save;
Then open the File menu again and Export as a PNG;
If you are on someone else's canvas, you may need to merge your layers first, and then copy that layer to a new canvas that you own before you can save it correctly.



