https://bugs.winehq.org/show_bug.cgi?id=56911
--- Comment #6 from Esme Povirk madewokherd@gmail.com --- Yep, the Mono component is for the main branch on gitlab which is a fork of cross-platform Mono, not Wine or Wine Mono. That does indeed use System.Windows.Forms from the Mono codebase.
I do plan to look into this, just haven't gotten around to it yet.