Rinse and pick over beans; place in a large pot, cover by 3 inches water, add salt, and soak for 8 hours or overnight.

Wash collards thoroughly; remove thick stems and coarsely chop; slice collard greens and set aside until needed.

Heat olive oil in Instant Pot set to high sauté. Add half the onion and cook, stirring often, until onion begins to brown. Add collard stems, ham hocks, bay leaves, ham base if using, and 8 cups of water. Seal pot and pressure cook on high for 45 minutes; allow pressure to release naturally for at least 20 minutes. Remove ham hocks and set aside; remove broth and set aside.

Dry pot, add bacon grease, and set to high sauté. When hot, add sausage and cook, stirring occasionally, until sausage is well browned. Using a slotted spoon, remove sausage to a platter, leaving oil behind. Add onion, celery, bell pepper, garlic, and green onions to the pot and cook, stirring and scraping up any browned bits, until the vegetables are soft and beginning to brown, 8 to 10 minutes. Add reserved sliced collard greens, 1 cup of the reserved broth, seal the pot, and pressure cook on high for 45 minutes. Carefully release the pressure after 5 minutes.

Drain beans; add to collards along with diced ham, salt and pepper to taste, thyme, and remaining reserved broth. Seal and cook under high pressure for 15 minutes; allow pressure to release naturally for 20 minutes. Carefully remove the lid and stir in diced tomatoes, parsley, and browned sausage; taste, and add salt, pepper, and cayenne as desired. Cover for 15 minutes with pot set to warm, then serve over hot cooked rice. Pass hot sauce at the table.