Since many editions (like 5.1.x.x, that I used since recently under Ubuntu until I installed 6, where I hoped my problem had been addressed) I seem to be unable to enter regular expressions in the search input field because every time I enter a square bracket or a backslash, the input field is emptied and only the backslash or opening square bracket character remains. My work around is to write regular expression in gedit (or another text editor) and copy & paste it into the search input field of libreoffice writer, but that I find not overly elegant.
That is really weird. I have been using LibreOffice in Ubuntu for years (back to 4.x?) and have never experienced this behaviour. Have you ever tried isolating your session from your user profile? It seems this is not related to hardware, or system, and there’s no related bug that I can find. And “auto-correct” options don’t operate in the “search” input field… Very odd!
Are you sure you do not have any keyboard shortcuts in LO that use these keystrokes?
@Xoristzatziki1 - I tested on my system, and LO’s keyboard shortcuts don’t operate (for me!) in the “Search” input field. And the problem can’t be at system level since the keystrokes aren’t a problem in gedit. This is really weird.
Take a look at the guidelines at https://wiki.documentfoundation.org/UserProfile to see if it can be caused by corruption in the user profile.