If you find packaging issues (like in this case), bug reports are the best place to report. Even better would be a PR with the needed fix 🙂
Kernel is already build with the needed settings, so bubblewrap will be adjusted.
Without reports, it is hard to know of bugs (or fix them), personally not a user of Flatpak.
https://kaosx.us/docs/bugs/
https://github.com/KaOSx/main/issues