[ern0]

On Amiga, there was a 3D demo with this trick. You can "jump in" your eyes to the proper position if you hold your finger at the place where the 3d image should appear, ca. 10 cm close to your eyes, and focus on it. You'll be cross-eyed without knowing it.

Also, I was using the trick as a "cheat" when I played Tiny Lands on Nintendo Switch, it's a "spot the difference" game, but with 3d landscapes (you can rotate and zoom): https://www.dekudeals.com/items/tiny-lands