This page of the guide to Far Cry 6 contains a detailed walkthrough of the Treasure Hunt for Mimo Abosi's Triada Relic available in El Este.
Subregion: La Joya.
District: Catalina Ridge.
The mission will begin when you read the note next to the closed door.
To get inside, simply shoot through the lock.
Go deeper into the cave - you will see water that you must dive into and swim to the next section. The water is under high voltage, though. You must return to cut power from the cave.
Exit the cave and track down the red object covered with wooden pallets. Destroy them and unplug the cable. This will remove the electricity.
Jump into the water and swim to the next part of the cave. Your task is first to go to the room with the blue door, where after using the correct button you will clear the elevator.
Open the elevator door, hook the climbing rope and drop down to the bottom of the cave. There you will find the enchanted object that will complete this quest.