[2024] Is altar of oblivion the final endgame boss(es)?

Hi, I've done all the 'islands' (alternative timelines) and I've got 12 Harbinger eyes. Now, Orenthia asks me to use them as keys to open the portal at the corner. I've done it five times, and I seem to find all the same boss(es) with some rare uniques as loot.

What's the point of doing it 12 times? Is it a part of the endgame farming design: 1. farm more Monolith with timeline bosses to get more eyes 2. and then repeat farming the Altar of Orobyss for its rare uniques if I need some for my build? I'm guessing here because none of the guide videos I've seen so far regarding LE endgame talked about this altar.

Except for Monolith -> Altar (if my guess is correct), Arena, and Dungeons, of course, plus endless gear farming (and relevant crafting/upgrading afterwards), is there anything else I'm missing for the endgame? Thank you.