When upgrading from Portainer Community Edition (CE) to Business Edition (BE), we perform a number of actions on the Portainer database to provide the additional functionality available in Business Edition. One of the BE-exclusive features is Role-based Access Control (RBAC), which provides a more powerful user permission experience.
For security reasons, when the upgrade to BE is performed, any existing users with the Standard User role (ie, any users that are not administrators) are assigned to the Read-Only User role. This can of course be changed per-environment after the upgrade.