There are several collectibles in Borderlands 4 that you can find to get specific rewards and upgrades. They are not your usual collectibles like Marcus Bobblehead, but are in the form of Evocarium. Getting them can be time-consuming but eventually worth it for the rewards.
All Harper’s Hideaway Evocarium Orb Locations Borderlands 4

The Evocarium in Harper’s Hideaway is found in the southern section of the area. Since Harper’s Hideaway lies just west of the Stockroom Order Silo. This is the location where you find a Vault Key and I think you would have come across this area already early in the game while exploring Fadefields.
Once you reach Harper’s Hideaway, head to the southernmost building and climb up to the roof. You’ll find the Evocarium shrine waiting there. Interact with it to trigger the beam which then guides you to the location of the three orbs.
Easter Orb Location

Follow the eastern beam and climb the stairs beside the house. Get up on the silo’s roof and jump across to the building’s rooftop, and you will get the first orb.
Northern Orb Location

After getting the first orb, jump onto the house ahead and go around it to the right. Follow the platform, and you will soon enough spot the second orb at once.
Western Orb Location

After getting the 3rd Orb, turn around and get on the building’s roof. You will see a tower below. Jump over there and you will get the last orb.
Once you have collected all three orbs, head back to the Evocarium and activate it. You have now unlocked unique recording and some Ordanite to increase the SDU slots.