ChatGPT got it with less prodding, but I had to set it to "Pro" thinking mode (ChatGPT's version of Deep Think, I suspect). I'm sure Deep Think could get it with even less prompting.
I think your conclusion that they aren't really thinking doesn't hold. They're already there, it just costs more and time to get good results.
https://chatgpt.com/share/69a12666-64b0-8009-8dfe-59546ac400...
EDIT - Updated the link to include the full conversation. Note that I didn't change it to pro mode until the end, and eventually got tired of waiting and just told it "answer now."