I have checked the box “do not show this again”. I have changed to Libre in all default apps. Still pops up every time I open a docx.
This site is for questions and answers about LibreOffice usage. For Microsoft Word, go to a related site.
@gabix: this seems to be not a question about MS Word. It tells that OP has a problem with making LibreOffice the default for some file types, and no matter what they do, when trying to open DOCX, they get a pop-up from unwanted application (Word).
However, that is still not a LibreOffice-specific question, but is about Windows OS configuration (file associations management).
If you have gone to Default Programs in Control Panel, selected LibreOffice, and then clicked “Set All Defaults”, there are a couple of other things you might try. In the same Default Programs settings dialog, you can look for the .docx file format and see if it is still set to Word. If it is not, another thing you might try is locating a .docx in Windows Explorer, right clicking, and navigating the “Open With…” dialog, selecting the “Always use this program to open this type of file” checkbox.