Helix Ultimate and module Joomla and Page Builder

On cariocadance.it I had installed the Mega Inc. template. Then I had problems and I installed and activated Helix Ultimate for all pages (which I have been using for years).
The site works very well but I can no longer operate in some important sections of the backend: Site Template Styles (any template, even Cassiopeia) and Site Modules (any module at the opening tells me 'XML data not available').
I redid the site (2024.cariocadance.it) also creating a new database; everything works except for the module (in Convert Forms) inserted in the Page Builder. The same Convert Forms form, if called from the menu, works. And it also works in the module but not inside Page Builder. What can I do?