\version "2.22.2"
\language "english"

forceHShiftF = \once \override NoteColumn.force-hshift = -0.325
slashFlag = \once \override Flag.stroke-style = "grace"
ossia = \markup \small \italic "ossia"

global = {
  \time 2/4
  \key fs \major
  \accidentalStyle piano
}

ossiaPart = \relative {
  \global
  \stopStaff
  s4. \startStaff
  <<
    {
      \magnifyMusic 0.63 { \slashFlag as8*1/32\noBeam^\ossia
        as16*1/16[ cs fs] } as16. b32*1/2 | \stopStaff s8
    }
    \\
    { \forceHShiftF as,8*15/16 [  \hideNotes b8] }
  >>
  s4. |
}

\score {
  <<
    \new Staff = "ossia" \with {
      \remove "Time_signature_engraver"
      \hide Clef
      \hide BarLine
      \override BarLine.allow-span-bar = ##f
      \override KeySignature.stencil = ##f
      \magnifyStaff #2/3
      \override VerticalAxisGroup.staff-staff-spacing = 
        #'((basic-distance . 0) 
          (minimum-distance . 0)
          (padding . 1)
          (stretchability . 0))
    } {
      \ossiaPart
    }
  >>
}