Quote:File associations no longer work properly on Windows 10 after a buggy update. Windows won’t let you select certain applications as your defaults. We tested multiple PCs running the stable version of Windows 10, and they all had this problem.

This is a strange bug. It affects some applications, but not others. For example, Windows 10 won’t let you make Adobe Photoshop or Notepad++ a default application for images or text files. But you can make other applications, like IrfanView, VLC, or Google Chrome, your defaults.

For example, here’s what happens when we try setting Notepad++ as our default application for .txt files in Windows 10’s Settings app. Windows just ignores our choice and chooses Notepad as the default.

Full reading: https://www.howtogeek.com/fyi/microsoft-broke-windows-10s-file-associations-with-a-botched-update/