To include voting option in your mail you can use single-value extended property.
Extended properties allow storing custom data and specifically serve as a fallback mechanism for apps to access custom data for Outlook MAPI properties when these properties are not already exposed in the Microsoft Graph API metadata.
To use Single-value extended property you can Refer to this documentation.
Further you can refer to these similar posts-
Voting Option in Microsoft Graph API
Voting buttons using MS Exchange Graph API Java SDK
Hope this helps.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have further questions about this answer, please click "Comment".