Graph API does not support using complex/advanced/deep select. For example in the Mail Graph API Explorer you can select: from https://developer.microsoft.com/en-us/graph/graph-explorer?request=...
lindalu-MSFT
Microsoft
MicrosoftHi, we apologize for the confusion where to post your Graph feedback. This community was intended to be a temporary location to submit product feature suggestions between Microsoft moving off of UserVoice and the release of Microsoft's official Feedback portal app. Now that the latter is released, we encourage you to resubmit this great suggestion on the official Microsoft Graph Feedback portal at Microsoft Graph · Community.
Kind regards,
Linda
Microsoft 365 Developer Platform community steward