(I'm not trying to be shitty; I'd really like to know. I spent some time Googling about conventions for the `env` command, and examples of incompatible systems. The only ones I found were two old, proprietary Unices. I got tired of searching and was hoping someone who knows a few examples offhand could help me out.)
I'm not 100% sure on all of these, but every one of the dozens of Linux distros I've used has `/usr/bin/env`. macOS has it, and it looks like FreeBSD does, too, and so does NetBSD.
Who are the oddballs? Does it include any of the free Unices?