You're confusing several things here. The only x86 processor that didn't allow returning to real mode was the 16-bit 80286 - on all later ones it's as simple as clearing bit 0 of CR0 (and also disabling paging if that was enabled).

Nothing more privileged than ring 0 is required for that.

"v86" is what allowed real mode to be virtualized under a 32-bit OS. This is no longer available in 64-bit mode, but the CPU still includes it (as well as newer virtualization features which could be used to do the same thing).