If you use an array, things become much easier:

my @s;
$s[$_] = $workbook->add_worksheet( "cpze".$_ ) for 1..8;
# $s[0] remains undefined!
for my $i (1..8) {
        for my $r (0..24) {
                for my $c (0..4) {
                        $s[$i]->write($r,$c,$arrays[$i][$r][$c]); 
                }
        }
}
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