If you check steam, there's 2 or 3 portal games outside the legit 2 that are super fun. One valve even approved as canon IIRC. One of them you go back and forth in time with a third portal type. One of them is even multiplayer.

I made the mistake of trying to go back and play Portal 2 during the pandemic, and the themes of isolation, neglect, abuse and gaslighting just weren't as funny in 2019.

tbh it's better this way.
Why?
Because nobody could ruin the story on the 3rd attempt.
BUT asssuming they could make the 3rd installment a prefect fit to round it up: Gimme