\version "2.21.0"

\layout {
  \override Score.BarNumber.self-alignment-X = #CENTER
  \override StaffGroup.SystemStartBracket.collapse-height = #0
  \override Score.BarNumber.break-visibility = ##(#t #t #t)
  \override Score.BarNumber.Y-offset = 4
}
\new StaffGroup {\set Score.currentBarNumber = #300 \bar "" 1 1}