I would install a fresh new WordPress if I were you
and simply sit for 2-4 hours
and create everything you had on the ex page (text and imgs - NOT plugins, etc.)
because basically
your home page is one big page
and 95% of menus are anchors (#) that scroll down to XY section within the home page
only the last item in the menu is more special (Teatro in affitto) which leads to ?page_id=925
so you don’t need any plugins you had (or galleries and other things) - WP can do it by itself
as well as those few PDFs you have on “home” as links.
In short, you create a new WP and in most cases just copy-paste text, etc., from the old one
the easiest way is through the browser (or save the entire page through the browser on the local PC)
and then you open the saved page and from it copy-paste texts and images in the new WP while creating pages (logged in as admin in the new WP)
But before that of course, save the existing one as a backup or you already have it on your PC and delete the existing WP on the hosting and install a fresh WP on that domain.
I think it would be faster than wasting hours on the net looking for some plugins, fixing JS also, etc.,
because you don’t have a complex WP website with 501+ pages, but only 2 (home and the theater one)
if I see correctly 
or create a free subdomain - where you will experiment
and then try the new WP there and everything else
and when you are satisfied with it
if you know how, you can copy/move it to this official WP ptm.000 (change of WP home URL is mandatory)
You should be careful about the color of the background you choose so that the text is readable and not like this
and replace this picture because it is blurry
Other posts you don’t need e.g. :
