Our council agreed back in 2015 to license Office365 / Microsoft365 for all staff (2) and councillors (13), they are quick and cheap to enable/disable, and the email system / events revolve around the Outlook, calendar and teams facilities, that have been used really well throughout pandemic. - It was so much better than the adhoc systems that email and website providers made available at the time.
It's not cheap, but we wouldn't go back to not having it.
But if the Council hasn't actively decided to go that way, then no an individual councillor can't demand it.