Both Windows and Linux versions of Sigil can remember its maximized Window with those lines commented out, but I don't know the first thing about fullscreen. None of the methods or shortcuts for entering fullscreen mode have ever worked for Sigil for me on Linux (Cinnamon) or Windows. Ever. I'm not complaining, mind you. I despise fullscreen mode.
I'm pretty sure we'd have to do some sort of coding to fully support fullscreen mode for Sigil on Windows
or Linux.
EDIT: the incredible shrinking stacked dockwidget from
https://www.mobileread.com/forums/sh...1&postcount=99 still persists, I'm afraid (with or without these recently commented lines)