...or, if you want to retain the rest of your code as you showed it, just enclose the RHS of the assignment to $sorted in []s:

my $sorted = [ sort { 

                  $a->{level} <=> $b->{level}
                                 || 
                  [$a->{menuname} cmp $b->{menuname}
                  
                  } @$sqldata ];
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