From poking around it appears to just be PLANNER and just a silly marketing way of referring to it by showing up as Tasks in Teams. There is no app in our tenant named Tasks in Teams. To Do is an O365 app (we do not have any Windows apps for this installed) so how on earth is it possible for a migration from an on prem mailbox to EXO to wipe out data wily nilly? The post says you cannot use To Do if you do not have an EXO mailbox after a date earlier this year - this is not correct.I can use the web app without any issue with an on prem mailbox. We working on moving to O365 and I found this little gem of a post that says you will lose data if you are using To Do or Tasks in Teams.