How UiPath Office365 activity works
The Office365 UiPath Activities are using the MSAL library to perform calls to Microsoft Graph API in order to perform the automation and bring the requested information.
Microsoft Graph API is just an aggregator or a middleware that it forwards the calls to some other APIs that Microsoft has, like Azure Active Directory API, Exchange API, Sharepoint API, etc. Microsoft built this API, to avoid Developers in learning the specifications for the other APIs and to bring an easier and unified way to deal with the automation via API.
All information related to Microsoft Graph API and its endpoints can be found in here .