How do I make those soft, fluffy things transparent?

[rich2005]

I have no idea what LINE  Camera or PicsArt is / are, so going by the title.   "How do I make those soft, fluffy things transparent?"

First the source of the images, The ones posted are jpegs, jpeg does not support transparency. Is there any possibility that you can download a png version that might be partially transparent?

Using what is posted.
Normally, Adding an alpha channel Layer -> Transparency -> Add Alpha Channel then remove white with Colours -> Color-to-Alpha and adjust the opacity slider to suit works.  However too much white makes up the pink color and that method is not so good, too faded.

Try using a Layer mask Layer -> Mask -> Add Layer mask  Choose a white mask and paint a  black-to-white radial shape gradient to suit. When satisfactory, Layer -> Mask -> Apply Layer mask Remember to export your frame as a png to preserve the transparency.

example:  https://i.imgur.com/bUQcm2V.mp4

A radial gradient might be too regular for some of the images, Again using a white layer mask. Use an elliptical selection, give it a big feather Select -> Feather and fill with black.  Finish with Select ->None and Layer -> Apply Layer Mask. Export as a .png

example: https://i.imgur.com/2Cwbsgv.mp4