It seems like you have more freedom than you think you do. See this comment <https://news.ycombinator.com/item?id=49594824> Packaging software shouldn't change the license of GOS as such. If you haven't had already, maybe the free software foundation could provide you with assurance?
I guess it will make your life much easier if you wouldn't have to restrict yourself that much.
No, we're not talking about packaging software in our app repository (App Store) but rather software being included in GrapheneOS. If any GPLv3 software is included in GrapheneOS then that places more restrictions on how it can be used as a whole.