What is not true ?
Ok, a write access may be granted through personal-files but if you start doing so for krita and ~/.local/share/… then you’ll have to provide this for any snap as some people might like to use good-old-legacy paths to tinker-tweak their favourite app’s…
So I’ll ask that for gimp and ~/.cache/thumbnails to fix this → GiMP and thumbnails for .xcf files → but you’ve already answered and it sounded like a no.