How do I install inkstitch extension in inkscape-flatpak?

I’m running Inkscape as flatpak on Kubuntu 24.04 and I wanted to install.the Ink/Stitch extension, but somehow this doesn’t seem to work like it did on the apt/ppa version. I’ve tried the script install from inkstitch, and I’ve tried to manually copy the contents of the tar.xz to the extensions subfolder in home/.var/...