Error: Call to undefined function template_preprocess_webform_element_managed_file()

I had the same issue in my project:
Attempting to access a webform submission containing a dropzonejs field results in the following error.

Error: Call to undefined function template_preprocess_webform_element_managed_file() in template_preprocess_webform_element_dropzonejs() (line 13 of /modules/contrib/webform_dropzonejs/includes/webform_dropzonejs.theme.template.inc).

The issue is due to this deprecated function module_load_include, using the ModuleHandler::loadInclude() instead seems to resolve the issue for me.

This is also addressed in the larger D10 compatibility issue https://www.drupal.org/project/webform_dropzonejs/issues/3299484 📌 Automated Drupal 10 compatibility fixes Needs work