This members-only tutorial provides the steps to set URL of the first term of a post/CPT item as the post's/item's background image in the posts list output by a Repeater when using Oxygen.
Let's take a sample scenario.
Custom Post Type: faq Custom taxonomy for the faq CPT: faq_category ACF image field for faq_category: term_image (Return format: image array)
Requirement: Display faq CPT items in a grid with each item's background image set to the URL of term_image custom field of the first faq_category that's assigned to each item.