As I say, it deeply confuses me: "To choose to have no choice" seems akin to "to desire a state of no desire": https://www.egscomics.com/comic/2003-04-30

On the subject of not having a mental representation of what this means, I have also been pondering recently about "literally unthinkable thoughts", which may directly sound like the same kind of paradox, but is at the meta-level and about the same kind of (apparent) paradox (that isn't a paradox at all for the people using the terms in those ways): https://benwheatley.github.io/blog/2024/04/30-13.54.02.html