Windows 10 New Bug! Microsoft confirmed on 8 November 2018 that changing the default applications to open different files does not work for some Windows 10 users in the 1803 version.
Windows associates different file types, such as .txt, .pdf, or .jpg, .png, with specific programs that open or edit files when a user double-clicks or right-clicks a file and uses the "open with" ”.
All versions of Windows use some default applications to open different file types. Text documents (.txt) are opened in Notepad by default and the images are in the Photos application.
Users can change file associations so that files open with their preferred applications. Text documents could, for example, open in Notepad ++ and images in an image viewer faster than the Microsoft Photos app.
Windows 10 supports two main options for changing file associations in the menu. Links can be modified from Settings - Applications - Default applications or with the "Open with." Menu.
This particular operation does not respond when administrators and users try to change the file associations in Windows 10 of the 1803 version. There are even some who report the same error in the latest 10 version of Windows 1809.
Although Windows allows you to use another application, after saving the settings are restored to their original state.
Microsoft recognized the issue and added it (and this, along with the others) to the list of known issues KB4462919 which was released on 9 October of 2018.