Here are the hardest indie puzzle games!

From the article. I added links to steam.
I am not sure I would call all of them indie games

(9. Braid
(8. Fez
(7. Antichamber
(6. Return Of The Obra Dinn
(5. The Talos Principle 2
(4. Isles Of Sea & Sky
(3. Portal 2
(2. The Witness
(1. Baba Is You