The newsletter forms (Optin addon in SP Page builder) are not working, they show the following message "Some problem occurred, please try again."
This problem also happens in your template, PITECH, Rythm and I suppose that in the others as well, please Check if it is a problem due to Mailchimp changes or in SP Page builder.
tested with SP Page Builder 3.7.14, Joomla 3 and 4, PHP 7.4.20