no luck with PyQt5 via pip. An error is reported here. If I was more familiar with Python, perhaps I'd know. I thought I had it working before with sip 5.5.0, or maybe it was some older 4.x. Didn't note that down so forgot.
https://bugs.kde.org/show_bug.cgi?id=444857
Not giving up but it has been sometime with various detours and setbacks. For now, I'm going to try all dependencies via MacPorts. Despite any lack of patches, maybe it'll work well enough. Otherwise, I might wait a bit before trying again.