Hi!
Is your question if purchasing Microsoft 365 will allow you to sync your Microsoft 365 account directly with Google Calendar? I am not the Microsoft support so I would suggest to ask them. But I haven't heard about a function in Microsoft 365 to sync directly with Google Calendar. I think you need an additional software to sync Microsoft 365 calendars with Google Calendar.
The desktop version of CalenGoo can sync directly with Microsoft Exchange/365 and also with Google Calendar. I.e. it can display both types of calendars. But it does not sync between them, it keeps them separate from each other.
Please don't hesitate to contact me again if you have further questions!
Kind regards
Dominique Gunia