From Pathfinder Lost Omens Character Guide, which isn't enabled.

Knight in Shining Armor

FEAT 12

Prerequisites Knight Vigilant Dedication; expert in light armor, medium armor, or unarmored defense; trained in heavy armor

As a knight in shining armor, you train daily in the heaviest armor, expanding your expertise to heavy armor. You gain expert proficiency in heavy armor.

Pathfinder Lost Omens Character GuideOGL