http://bugs.winehq.org/show_bug.cgi?id=26549
--- Comment #9 from Ken Sharp imwellcushtymelike@gmail.com --- There's been a number of commits apparently related to this https://gitlab.winehq.org/wine/wine/-/commits/master?search=priority so I thought I'd give it a try in Wine 10.12.
Tried "start /belownormal notepad" but notepad runs with normal priority, though that might be related to start.
Tried running BOINC with Einstein@Home and the client application runs with normal priority on all threads.