I've seen several complaints here about how GOS does "user profiles", specifically complaining they make the UX too poor. There is a weaker form of user profiles called "work profiles" that one can use to have separation between apps but in a more user-friendly way.
Private Spaces are available since Android 15 and provides a similar nested profile without the need for a management app. They're better integrated into the OS user interface.
Secondary users, work profiles and Private Spaces are standard Android features but GrapheneOS does provide improvements to secondary users and Private Spaces such as control over clipboard sharing with a Private Space, enabling having a Private Space for each secondary user, cross-user notification forwarding, etc. https://grapheneos.org/features has a good overview of most (not all) GrapheneOS features.
The recommended app is "Shelter". https://f-droid.org/en/packages/net.typeblog.shelter/