Thank you T-P for your answer.
I think my post was not clear.
My problem is just with “google chrome browser” version 78.
Under chrome i can’t edit or add page or post but it’s working only with classic editor and when i switch to gutenberg i have a blank screen.
With “firefox”, “opera”, “safari” i have no problem to edit or add pages and posts with classic editor and gutenberg.
Regards,