Diverging my eyes is very easy and painless. Crossing my eyes kinda hurts.
This is probably because I’m nearsighted and don’t use my glasses when using my phone and instead hold my phone 20cm from my face. They’re already crossed from doing that and crossing them even more is difficult.
Diverging your eyes is how magic eye posters work.
Here is a tool from Reddit user vibrunazu to convert between Cross View and Parallel View: https://vib-xibot.web.app/
Honestly, it probably wouldn’t be terribly difficult to make a bot to automate the process. Every time there was a post on CrossView, the bot could (optionally wait some grace period to give the OP a chance to post the parallel view post themselves and) just grab the image, cut it in half down the center, swap the two halves, and make a new post with the resulting image on the Parallel View community. As well as vice versa for those who prefer the cross view. Of course, it could ignore posts without images (like this one).
Just a thought. I haven’t delved into looking into how to make a Lemmy bot, but I can’t imagine the real “business logic” of this one would be difficult.