Note: this list is generated by looking for the string for this theme hook, so it may include some references that are not actually using this theme hook.

BlockHero::form in core/modules/layout/includes/
Builds the block's configuration form.
file_field_widget_form in core/modules/file/
Implements hook_field_widget_form().
file_theme in core/modules/file/file.module
Implements hook_theme().
file_upload_validators_pre_render in core/modules/file/file.module
Pre-render callback for adding validation descriptions to file upload fields.
filter_format_editor_link_form in core/modules/filter/
Form callback: Display a form for inserting/editing a link or uploading a file.
image_field_widget_form in core/modules/image/
Implements hook_field_widget_form().