Planner with Exchange Hybrid

from MS documentation it is unclear what works and not with Exchange Hybrid 

I can see a lot of "may" but no definitive answer and what the variables are

• If your organization is not using Exchange Online for your account, you may not be able to comment on tasks in Planner. https://support.microsoft.com/en-us/office/comment-on-tasks-in-microsoft-planner-fd4aedde-7785-4cd0-96ee-122fbc9140e1
• Planner has full functionality when your user has a product license that includes Exchange Online. Planner users without Exchange Online may have issues with viewing or adding comments to a task. https://docs.microsoft.com/en-US/office365/planner/planner-for-admins#can-people-in-my-organization-use-planner-if-they-dont-have-an-exchange-online-mailbox
• email will only be sent to users who have a product license that includes Exchange Online. Users at organizations using on-premises Exchange Server or hybrid configurations may not receive all Planner emails. https://docs.microsoft.com/en-US/office365/planner/planner-for-admins#how-do-i-make-sure-all-my-users-can-get-emails-for-planner