Item description:

Interact with the Red Arch doorway
(Cursor already on it - press X)

NOTE:

This is a timing puzzle

You need to choose between two paths
on each screen (3 screens in total)

If you just keep spamming X on the default path,
you'll eventually get through

Reidso's Note:

I had created a backup save on the 3rd screen,
but when I reloaded save, the game wouldn't
let me to continue