https://wccftech.com/dark-theme-to-do-users-windows-10/

Microsoft is bringing dark mode to its To-Do app for every Windows 10 user. This theme went live for Windows 10 Insiders last week, however, it is now also available to non-Insiders through an update to the app according to the folks at WindowsCentral. The new update brings the following changes to the app along with the Dark Theme.

You can get to try this Dark Theme by updating your To-Do app to version 1.33.11732.0 via the Microsoft Store.