Changing default application for plain text file
 

On a Debian 12 Live system the default application for plain text file is LibreOfficeWriter. How can I change that programmatically to, for example, gedit editor?

You should be able to right click on a text file then choose Properties.
If that doesn't work, use update-alternatives or
Another way:
xdg-settings set default-web-browser name-of-browser.desktop
well you would use the editor you want to use.