I tried to push to the MAS and it was rejected because my StatusBar icon didn't support the current "Use dark menu bar and dock" setting.
Well, last week I submitted new versions of two apps of mine that make use of StatusBar with several icons; but the reviewer did not say anything. In a few hours both the apps were "ready for sell".
BTW, the two apps are still 32bit and for the StatusBar I use of macoslib.
As for the icons, they are just plain .png; and I apply them directly from the Resource folder of the app, something like:
myStatusItem.image = picture.open(f)
where f is the pictureFile in the Resources folder.
I wonder if I was just lucky.