I just booted OpenBSD 7.0 (which is a bit dated).

The find utility has print0, and xargs has -0. Notibly, xargs also has -P for running processes in parallel.

rm has both -d and -v.

The renice command appears to be able to use relative adjustments with -n.

There is a timeout command.

There is a readlink command, but no realpath (but a manual page exists for it as a system call).

Strict adherence to POSIX isn't a goal of any of the current BSDs is it?

I'm confident they'd accept patches.

macOS

People get "POSIX compliance" confused with "Unix certification". The first is an API you implement, the second is a rubber stamp.

All active Unix-like operating systems aim to implement the new interfaces as they're defined.