Maybe try to create a font object like the following. The fontCreate is in "perldoc Tk::Font" ( I have found the 'bigfont' to work on linux and windows.)

my $font = $mw->fontCreate('normal',
              -family => "helvetica", 
              -size => 24, 
              -weight => "bold");

my $bigfont = $mw->fontCreate('big',
            -family=>'courier',
            -weight=>'bold',
            -size=>int(-18*18/14));


my $info_frm = $mw->Frame(
         -relief => 'groove',
         -borderwidth => 2,
         -label => "This application is to install Libs",
         -labelFont=> 'bigfont')
              ->pack;
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