Can plain-box window remove default boards?

I create a plain-box (style) window. but not willing the default board of it.

a no border,no min/max/ button window is what i want.

I suppose you are trying to do that under Windows 10 where there is currently a bug that shows a white bar on top.

I filed a bug report back in July last year (XOJO ? ? ? PLEASE ? ? ?)

You will find a workaround there : feedback://showreport?report_id=40171