Hello again.
I would like just to update in case someone has /will have the same problem.
I did the change initially and I didn’t have significant changes.
At the same time, I tried again the debugging tips.
The problem seems to be for me this plugin “Social Icons Widget & Block by WPZOOM” which was installed on many websites.
My wrong was that I didn’t even deactivate it,when I checked the first time, as I considered it a “GP- plugin” because came as theme requirement.