In October of 2017, Microsoft released a version of Windows 10 called the "Fall Creators Update," back when the company tried to give brand names to these things rather than just sticking to version numbering. One of the new apps included in that update was called Paint 3D, and while it shared a name with the old two-dimensional MS Paint app, it was entirely new software that supported creating 3D shapes and a whole bunch of other editing and transform options that the old Paint app didn't have.
For the briefest of moments, Microsoft planned to deprecate the classic 2D version of the Paint app and focus its development resources on Paint 3D. But user outcry prompted Microsoft to cancel Paint’s cancelation and move it into the Microsoft Store for easier updating. The company soon began adding new features to the app for the first time in years, starting with keyboard controls and extending to a redesigned UI, support for layers and PNG transparency, and integrated AI-powered image generation.
But the old Paint app's renaissance is coming at the expense of Paint 3D, which Microsoft says is formally being deprecated and removed from the Microsoft Store on November 4. Windows Central reports that users of the app will be notified via a banner message, just in case they aren't regularly checking Microsoft's documentation page for the list of deprecated and removed Windows features.