When you look at the title of the file you can see it in an input box yet you cannot input any new keys, there is even a cursor there which indicates to be that if I press a key on my keyboard it should react in the same way a “word” program would.
There is a point in what you wrote. Changing the file name in this window is indeed not possible.
May I propose to file a bug report here: https://www.libreoffice.org/get-help/bug/