Well, I found the solution to my problem.
Having created my theme myself, I put the following line in my function.php file
add_theme_support (‘post-thumbnails’, array (‘post’));
Before 5.4, I had no worries.
Since update 5.4, it made me disappear the possibility of putting a company logo.
I removed it and it works again.
In addition I kept the possibility of putting a featured image on a Page or an article.
Hopefully it can help some people.