On Web, you can duplicate lists and tasks. On Windows, you can duplicate lists but not tasks.
Basically you can have templates for lists and duplicate them on both Windows and Web.
An error occurred while saving the commentLawrence Liu commented
1. Sign in to the Windows Outlook desktop app with the same Microsoft account that you use with Microsoft To Do.
2. Switch to the folder list view by selecting CTRL+6, then expand the folder "Tasks". You should see your tasks folder now as well.
3. Right-click on the task you want to copy, then select the option "Copy".
4. Ctrl+v to paste the copied task.