Technically, Owner doesn't have access to list all installed apps for other profiles, but apps with system-level privileges can.
For example, when logged in to Owner, you can list all installed apps for every profile in the Settings app by going to Settings > Apps > All apps. There, in the code, there's logic for something like "if logged in as admin, list all apps for all profiles". To do that, the app, Settings, needs the permission
INTERACT_ACROSS_USERS_FULL, which is a permission restricted to apps that were included in the OS.
I seem to recall some Google apps use this permission on Stock, but they 100% cannot get this permission on GrapheneOS. No non-system app installed in any profile, including in the Owner profile, can list apps installed in other profiles.
I don't know for sure, but as far as I can tell Settings can list any profile's installed apps while logged in to any profile, even if it's not Owner. Technically, that's what Settings can do with its permissions, but in the places I've checked, AOSP code is careful to restrict this kind of usage to the Owner profile. GrapheneOS devs have done the same when changing Settings' code as well.