Use this code example to allow Formidable text field to be mapped to an ACF email field.

add_filter('frm_acf_supported_field_types', 'acf_map_text_to_email');
function acf_map_text_to_email( $field_types ) {
	$field_types['text'][] = 'email';
	return $field_types;
}

To map a user ID to an ACF user Field:

1. Add a hidden field to your form https://formidableforms.com/knowledgebase/hidden-field/
2. Set the default value of the field to [user_id]
3. Add the code snippet below to your site:

add_filter('frm_acf_supported_field_types', 'acf_map_hidden_to_user');
function acf_map_hidden_to_user( $field_types ) {
	$field_types['text'][] = 'email';
	return $field_types;
}