Brienne is right.
Under your last folder (before Groups) click on "More".
This will take you to the Folders side window. On top you will see your "Favorites" folders, under that will be your login name and the same list of folders as are shown in "Favorites".
Right-click on the folder that you want to rename that is listed under your name.
You will then see the option to rename. Once you go back, the folder is renamed.
I completely agree about Microsoft Flow. It's the only working way I've found to integrate Outlook 365/Outlook.com integration with Google Calendar). Microsoft Flow is a service similar to IFTT, except geared to work with Office 365 services (and IFTT can't do this).
Here's a bit more information:
The free level of Flow allows for 750 "events" per month. Events are triggered when a change is made on either of the calendars, so unless you update your calendar an average of more than 25 times per day you will be OK.
You will need to sign up for the free service and activate two "templates":
Either: "Google Calendar to Outlook 365 Online Calendar" & "Outlook 365 Online Calendar to Google Calendar" sync
OR: "Google Calendar to Office.com Calendar" & "Office.com Calendar to Google Calendar". Depending which one you use.
As you may know, if you have Office 365 Online, it can also be linked to an Outlook.com address, so you can have the same synced calendar on both services, if you use both.
Use this Bit.ly link to check out the various templates related to Outlook:
https://flow.microsoft.com/en-us/templates/?category=eventsAndCalendar&sort=properties/statistics/instantiations Again, you will need to sign up for the free account before you can use them.
Also, you can see a really helpful step by step guide to setting it up here: https://shift.newco.co/sync-your-calendars-using-microsoft-flow-and-yes-google-calendar-works-too-a28be5a604dd
Best Answer
Currently, it is not an option in Outlook.com or the beta version.
However, Office 365 has more functionality, so it may be available there. So I have some suggestions ...
Places to look in Settings (beta version):
Places to look in Options (regular version):