There are three (3) types of users for GMB listings: Owner, Manager and Site Manager. Each of these has their specific roles and capabilities.
Owners: In every GMB listing, there can only be one (1) primary owner with several other owners as well as managers and site managers. They have full capabilities, from adding or removing users to downloading insights.
Managers: They have most of the capabilities of an owner but cannot add or remove users or remove business profiles.
Site Managers: They have limited capabilities and cannot add or remove users, remove business profiles, edit information, manage Google ad account links and use Messaging, among others.
(As of September 2021, Google has taken out Site Managers from GMB access levels. Please be guided accordingly)