Wow, this game is super well done! I got to the end and was only disappointed there wasn't more. The concept is simple and elegant, yet there is much to expand on and explore. I could see more interactable objects added in the future to increase complexity, or more intricate room layouts.
One thing I really appreciate is when games have really simple controls, and this game does that extremely well. I also want to highlight the music and sounds. It was really atmospheric and pleasant to listen to.
My one criticism is that it is rather unclear that when you take a portal it isn't guaranteed that the exit portal will take you back to the same portal you entered. Sometimes it does, sometimes it doesn't. I do see that it probably reduces visual clutter to have as few portals as possible, but it's just something to keep in mind.
Overall, wonderful work that has definite potential to go further than this jam!