Microsoft Graph APIs have improved consistently over the years. Step II, Give Target Application the permission for Graph API and/or SharePoint API in Azure Portal depending on whether you will access the site resource withGraph API, like, https://graph. If you need to use SharePoint APIs, for example, SPO Rest API, SPO CSOM, you give SharePoint API permissions. Selected Application permission, you can use Graph API to access the site. Selected Application permission, you can use SharePoint Rest API or CSOM to access the site. NOTE, For SharePoint APIs, you cannot use just client secret to do the authentication, you have to setup certificate to gain Access Token. To Test the access to specific site, you can use following sample PowerShell script to get App Only Access Token and retrieve the site with Graph API, see reference https://learn.
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Source: Microsoft Tech Community SharePoint Blog
