x86 (32-bit) multicore very slow, but x86-64 is fast (on macOS arm64 host)
Description of problem:
More cores doesn't slow down a x86-32 guest on an x86-64 host, nor does it slow down an x86-64 guest on an arm64 host. However, adding extra cores massively slows down an x86-32 guest on an arm64 host.
Steps to reproduce:
1. Run 32-bit guest or 32-bit installer
2.
3.

I have replicated this over several OSes using homebrew qemu, source-built qemu and UTM. This is not to be confused with a different bug in UTM that caused its version of QEMU to be slow.

This also seems to apply to 32-bit processes in an x86-64 guest.
Additional information:
https://github.com/utmapp/UTM/issues/5468