I attempted to add items to the #horse_food and #horse_tempt_items item tags using a datapack, and I discovered that they do not work as intended when compared to other mob food item tags such as the one for pigs. Right-clicking the horse with the newly added items does nothing, the horse neither eats the item nor gets ridden by the player. The horse does follow the player when they are holding an item in #horse_tempt_items, but it does not enter love mode when the player attempts to right-click the horse. These item tags were tested on both fully-healed horses as well as hurt ones with low health.

The expected behaviour is for the horse to eat the items from the #horse_food item tag to restore some hearts, and the items from #horse_tempt_items to make it enter love mode.

Attached below is a datapack that replaces the items in both tags with carrots. Upon enabling it in a world, the player will discover that carrots will not be able to feed any horse.

horse_tag_test.zip