stefanato1
Hi,
If I understand you correctly, you meant the custom fields of Joomla content, right?
If it's a text field, it can't display as dropdown in the filter of JA Megafilter. You can add custom field with type of "List" instead.
For example: https://ja-megafilter.demo.joomlart.com/index.php/joomla-custom-fields-filter#sort=name&sortdir=asc
As you can see in the left sidebar, there is a field called 'Value' , it's a custom field with type of "List": http://prntscr.com/oir3ak
And in the filter settings in JA Megafilter, we select dropdown type for it: http://prntscr.com/oir3jf
Regards