Utnik, looks like your suggestion to install on the Mac side worked. I installed the app on the Mac OSX side and though it gave me a few warning errors it did install and open:
~ App is not from the Apple store or from an approved vendor. Open anyway? (and of course I said yes.)
~ “Scribus” is not optimized for your Mac. (FYI-I'm running High Sierra v10.13.5, mid 2011. Apple will no longer allow me to upgrade the OS. Machine considered obsolete by Apple.)
~ This app needs to be updated by its developer to improve compatibility.
~ Ghostscript is not installed on your system, or Scribus is not configured with the path to the software. Until this is remedied, you cannot import EPS images or use Print Preview.
I encountered no error or such advisory messages when installed on the Win7 side.
I then opened the Mac app, created a test page, and when I went to do a Save-As there were two 'top-level' choices in the left pane: "Computer" and "Volumes". When I clicked on Volumes, I DID see my shared "X:\" drive.
I then went back to the Parallels/Win7 side and re-opened Scribus there and this time when I went to do a Save-As I saw in the same left-side pane that there were still the same two choices as before, "Computer" and "Ed" (my name). However without clicking anything I immediately saw my "X:\" drive appear. Maybe something caused the drive to be visible this time subsequent to installing and running the app on the OSX side first and then running it on the Parallels/Win7 side. I can only tell you what I encountered. Anyway, my issue on the Win7 side was solved by your suggestion to install it on the Mac side.
BTW, to answer your question, I guess the reason that I installed Scribus on the Win7 side is because that's where most of my apps reside, though I do use both OS sides on my Mac. I have 3 other Linux-Ubuntu machines running here at home and might even try installing the app there. I'm anxious to learn more about the Scribus application and grateful that there's a nice forum here that is available as a resource for us newbies to reach out to for assistance and help. Thanks. Ed.