I love Microsoft To Do, but it can sometimes be a bit flaky on a Mac. I started having the problem where it would crash on start up, it wouldn’t sign in correctly and I couldn’t change any settings or open preferences. Fortunately the clever clogs on the Microsoft community forum posted this solution and it worked for me! – Basically you have uninstall the app, remove all traces of it and start again. I’m currently on MacOS Monterey 12.7 and back on To Do!
Steps to fix Microsoft To Do on Mac – Sept 2023
1. Uninstall the To Do Mac app
2. Open Finder and press CMD+Shift+G
3. Enter “~/Library/Group Containers” – locate and delete the “UBF8T346G9.com.microsoft.to-do-mac” folder
4. Press CMD+Shift+G again
5. Enter “~/Library/Containers” and locate and delete “Microsoft To Do” folder
6. Restart your Mac, re-download the To Do app
7. If successful you can now log back into To Do
If this doesn’t work, then it’s probably back to Google to search for another solution!