> 64-bit kernel and 32-bit userspace
That's what the Raspberry Pi Desktop did.
It's the Pi project's x86 OS, a drastically cut-down Debian with LXDE. It was pretty much the smallest full-desktop distro I've seen.
(Excluding specialist things with window managers like antiX or TinyCore.)
Sadly never made it off Bookworm. I wish they'd update it, or someone took over maintenance.