I frequently have Alexa add tasks to Microsoft To Do. However, this stopped working for me a few days ago. If I ask Alexa to add a task, she responds that she's added it, but it doesn't appear in Microsoft To Do.
All of the instructions (e.g., here) say to set up Cortana on your PC and add the Cortana skill within Alexa, but Cortana has been deprecated so you can't get to her settings, and I no longer see Cortana listed as an Alexa skill. (And for what it's worth, I haven't messed with any of the To Do/Alexa settings in years.)