xaos doesn't use multiple CPUs

[martinwguy]

I've never seen xaos use more than 100% of one of the two available CPUs, no matter how big I make the window and deep the calculation.
This on Debian bookworm 32-bit. I've tried compiling 4.2.1 from git with the same result.
Even with -threads 32 "top" shows it using no more than one thread in one process.