\version "2.24.1"

music = \relative c'' { c1 \bar "|." }

small = \new Staff \with {
  \magnifyStaff #7/10
} { \clef treble \music }

normal = \new Staff \with {
% \magnifyStaff #7/10
} { \clef treble \music }

\score {
  <<
    \small
    \normal
  >>
}