Hello,
I am new to Linux and KDE. I am not sure this is a bug or not. I usually create a "Plain Text Document" using my right-click menu, i.e. using Right-Click> Create New> Text File. Everything works fine before, a plain text document is created. However, when I create a new text file today, it automatically turn its extension to *.ui . It is described as "Qt Designer File". I have no idea what I did wrong, but I can no longer create "Plain Text Document" using "Right-Click> Create New> Text File". I am really confused.
Could someone tell me how to solve this issue as I do not have any technical experience.

I reproduced this as following screenshots:

[img]
https://ibb.co/QQfSd9W
https://ibb.co/TmQJhDS
https://ibb.co/9qWSvYD
https://ibb.co/BrCKPcX
[/img]

Hi!

Without looking at the pictures, I guess you've recently changed some mimetypes or templates. The file extension is nothing you can rely on. You can even name your file myfile.shouldbedone and it will trigger the same application to open (see `man xdg-open` for details).

The .ui extension is used by QtCreator (or KDevelop) to describe xml-files used to specify GUI-design.

As you did not mention what distribution you are using, I'm linking you to different ones to give you a starting point:
* ArchWiki - XDG User Directories
* ArchWiki - XDG MIME Applications
* UbuntuWiki - FileTemplates
* DebianWiki - MIME