HI MB132_997,
Good day!
Thank you for posting to the Microsoft Community. We are glad to assist.
As per your mentioned description about "Cannot Delete Tasks from To Do". To understand the situation and be able to offer you relevant suggestions, we would need a little more information from you. Kindly help us by providing the following information:
1- Could you please provide us product and version details of your Outlook? About Office: What version of Office am I using? - Microsoft Support and What version of Outlook do I have? - Microsoft Support
2-try join in safe mode: Open Outlook in safe mode
3- May I please confirm that you get the same situation when you open Outlook on the Web (https://outlook.office.com) in a private window or another browser?
4- try the delete steps in the Microsoft article: Create, edit, delete, and restore tasks
This requested information will help us to narrow down the scenario and find the right troubleshooting.
We are looking forward to your response! Thanks for your precious time. Have a nice day!
Best Regards,
Microsoft Community Moderator