Calm down. Breath.
Most Microsoft customers are close to whiplash from the constant head-shaking over Windows bugs the last couple months. This latest one isn’t earth-shattering, but it still helps highlight Microsoft’s lack of Windows quality and the fact that Windows-as-a-Service is failing.
A recently discovered bug in Windows 10 keeps certain applications from being selected as the default for the file association. Microsoft has now updated the KB articles for the recent updates:
KB4464330 – Windows 10 version 1809
The KB articles have been updated with the following known issue:
After installing this update, some users cannot set Win32 program defaults for certain app and file type combinations using the Open with… command or Settings > Apps > Default apps. In some cases, Microsoft Notepad or other Win32 programs cannot be set as the default.
In some cases, attempting to set application defaults again will succeed.
Microsoft is working on a resolution and estimates a solution will be available in late November 2018.