There is no single endpoint to cover that. Each workload has its own settings, and only SharePoint Online's are currently queryable via the Graph API:
GET https://graph.microsoft.com/beta/admin/sharepoint/settings?$select=isLegacyAuthProtocolsEnabled
The Get-OrganizationConfig, which returns Exchange Online's configuration, has no analog in the Graph API. So you have to use PowerShell if you want to report on these settings.