Appoggiatura or grace note before a bar line
By default, appoggiaturas and grace notes that occur on the first beat of a measure are printed after the bar line. They can however be printed before, simply by adding an invisible BarLine and then the visible one, as demonstrated here.
\version "2.24.0"
{
R1
%% default
\appoggiatura d''8 c''4 r2.
%% cheated
\appoggiatura { \bar "" d''8 \bar "|" } c''4 r2.
}