while using notepad++ for more than 3 years, when saving files in the past, I have been able to assign my own file extensions to my files.
Since the last update, when I try to save a new file with my own file extension, Notepad++ v7.8.8 saves all of my files as file.ext.txt and saves it as a text file type.
This is a problem for the applications that I am working with.
Just change the Save as type field to
*.txt, and it will accept the extension you type.