[BizarroLand]

I get that whoever made and posted that terrible youtube short is annoyed, but if they had done a basic search online, specifically "how to edit a brush in gimp", the first result would have taken them to this page:

https://docs.gimp.org/en/gimp-brush-dialog.html

Which says:

It is a general rule that you cannot alter the resources that GIMP pre-installs for you: brushes, patterns, gradients, etc; only ones that you create yourself.

It's okay to be annoyed when something doesn't work the way you want it to, but RTFM before you make a rant about it. It's the bare minimum.