[Solved] 0: Call to undefined method Joomla\...\SiteApplication::isSite()

After I migrated the last site still in Joomla 3.x to 4.4.3, the PageBuilder type modules are no longer visible.
They prevent the page from loading and only the error in question is shown.
If I try to edit the module in the administration panel, I cannot open it and the same error is shown.
It is the only site of mine that shows this behaviour.
Do you have any suggestions?

Hi
is Page Builder CK up to date ?
go in your website config >> system >> debug >> set it to YES
then give me the error message that appears so that I can track the source

CEd

The version of Page Builder CK is 3.3.4. No newer version reported for Joomla 4.4.3.
I activated the Debug mode, but the error is very long.
You can see it here .
Thank you.

ok please go in your plugins >> pagebuilderck type >> search for "contact"
you must disable it and use only "contact2"
you may need to redo your contact form as the "contact" plugin is very old and must not be used anymore

Done. It works.
Thank you so much!