GetProcessGroupAffinity requires [overaligned aligned memory GroupArray]

Is this (bug?) documented anywhere?

Outside of the fio comment you linked, this StackOverflow question was the only place I found that recorded it. Somehow Microsoft also became aware of it (see below)...

Is this even a bug?

Microsoft's legendary Raymond Chen posted a comment on your question confirming it's a bug. Further it's been fixed in Window 11 sometime between 2023 - 2024:

This bug was fixed in Windows 11 last year, for the record.

Raymond Chen, Nov 9, 2024 at 5:33

(Thank you @sopel for posting this and thank you @raymond-chen for taking the time to acknowledge the issue and explain it's been fixed)