With LibreOffice, all the applications, Writer, Calc...
Since years, it was the case, previously to OS Zorin, with Ubuntu!!!
And today on Zorin OS 17.3 Pro, in X11 mode
When I want to save my work with the command Save As
I did not see repertory and files !!!
I can select them, see the image below, but I don't know which files I have selected.
Thank you for your feedback.
José from France 
Salut,
Est-ce que tu as installé un thème personnel ?
Hmm ... this looks for me more like a Theme Issue - especially with Light and Dark.
Do You use a Third-Party Theme or have You used one?
Or did you made some changes /adaptations for a theme in the gtk.css files at ~/.config which has an impact on all themes you use?
I had a similar problem (caused by myself) recently and it helped to take a look at my settings in that files.
The problem happened only in the light themes, not in the dark themes, because I had set a white font color there (for the titlebar in my case).
You could test if you can see the files when you select a dark theme or another theme for the applications.
Merci de ce retour rapide.
Non, et en même temps je vérifie
En général, j'évite tous ces paramétrages, extensions...
Je suis revenu sur Zorin !!!
Même problème
Thank you for your time.
Yes, and now I am back on Zorin
(previous answer to @Nourpon)
From my side, this day starts very well!!!
It works !
The answer was here:
Did you already try the option to use the system’s dialogues for Open/Save?
See > Tools > Options > LibreOffic > General
I deselect the box. And it Works 
Very strange... It was the case with my previous Ubuntu
Nice day for everyone :).
Note 1: I select it again. Same issue. Files hidden.
Note 2: To do individualy for each LibreOffice application: Calc, writer...