You really can’t to this with ACF. ACF has no way to show images from a certain term.
I would build a shortcode and skip ACF entirely by doing a query to get the images in the term.
If you really want to do this with an ACF gallery field you could create an acf/load_value filter (priority > 10), ignore whatever value the field has do the same query and return an array of attachment IDs. Basically this makes the ACF gallery field just a placeholder. You’d probably also need to add another field to set the term to use for the gallery and get/use that value in the query.
