\version "2.23.80"

rightHand = { \repeat unfold 16 { c'16 } }

leftHand = \relative {
  % Remove the markup and all is well
  \clef bass g,8\noBeam^\markup \large \italic "leggierissimo"
    \clef treble <b' f' a>8 q2.
}

\paper {
  ragged-right = ##f
}

<<
  \new Staff \rightHand
  \new Staff \leftHand
>>