Pretty sure there is no way to export system settings. I don't expect that is a feature GrapheneOS will prioritize. However when Seedvault eventually gets replaced, maybe the settings will be backed up more correctly.
User profiles do not share settings because they are meant to be completely isolated. It would be tricky to correctly keep settings in sync because different users are unlocked at different times, and it would probably weaken the isolation.
If you want different profiles to have the same settings, expect to configure them as such manually.