Are there any solutions for implementing a more granular admin access in 3CX? How could we go about implementing multiple admins with different access levels? Can this be done?
If you're referring to managing extensions or giving additional users account-wide Admin rights, @Saqqara's link should help.
If you're referring to managing call flows including Ring Groups, Digital Receptionists, Queues or Settings, unfortunately there isn't currently a way to provide user's with access to those items without giving them full Admin access to the entire account.
However, there is a post in the Ideas forum requesting this type of granular controls. If that is what you're needing, please vote for the idea and add any relevant concerns/requirements there. https://www.3cx.com/community/threads/3cx-management-console-more-granular-delegation-rights.52853/