My memory is failing me on this, was going to try it tonight, but if someone can remind me - can I build a pex for a Linux x86 box using my x86 Mac (using platform/complete_platforms)? Or do I need docker involved?

You can if there are wheels available for x86 linux for all the transitive requirements. In 2.17.0.dev0 this will still work if there are sdists that are not platform-specific in practice, i.e., it'll work in all cases where it could possibly work.

Ah right right, I think that was the issue last time, something about transitive requirements