If you want the Target.xlsx workbook to have a worksheet for each of the different workbooks/worksheets try this

#!/usr/bin/perl
use strict;
use Spreadsheet::XLSX;
use Excel::Writer::XLSX;

my $target = 'Target.xlsx';
my @file_list = glob "*xlsx";
my $workbook = Excel::Writer::XLSX->new( $target ) 
   or die "Could not create $target : $!";
 
for my $file (@file_list){
  next if ($file eq $target);
  print "Scaning $file\n";    
  my $excel = Spreadsheet::XLSX->new($file);
  for my $sheet (@{$excel->{Worksheet}}) { 
    my $name = $file ."_".$sheet->{Name};
    my $worksheet = $workbook->add_worksheet( $name );
    print "Copying $name\n";
    $sheet->{MaxRow} ||= $sheet->{MinRow};
    $sheet->{MaxCol} ||= $sheet->{MinCol};
    for my $row ($sheet->{MinRow} .. $sheet->{MaxRow}) {
      for my $col ($sheet->{MinCol} ..  $sheet->{MaxCol}) {
        my $cell = $sheet->{Cells}[$row][$col] ;
        if ($cell){                   
          $worksheet->write( $row, $col, $cell->{Val} );
        }
      }
    }              
  }
}
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