Up until Windows 11 came out, Notepad was one of the least changed Windows apps. It is still a barebones text editor, but it has learned a few tricks in Windows 11. A developer was able to port Doom to Notepad in order to qualify it as a gaming platform.
There is a new tabbed user interface for the Notepad app that is being tested by Microsoft, as well as another new Notepad feature. After it was posted, it was deleted, but it was preserved by outlets like Windows Central that caught it before it was taken down.
It's possible that this tabbed Notepad won't ever be released by Microsoft, but it's also possible that it will end up in the public builds of Windows eventually.
Windows 11 and its apps are updated on a "whenever we feel like it" schedule, with both major once-a-year updates and periodic feature drops. We won't need to wait for the big update to get this version if Microsoft deems it ready for release.