FILE:
while (my$file = @files) {
    for my $kp (@KEEP) {
        next FILE if $file eq $kp;
        
    }
    rmtree($deletes);
}
  return;
}

##</code><code>##

my %keepers = map {$_=>1} @KEEP ; # OR declare %KEEP instead of @KEEP
rmtree ([grep {not $keepers{$_} }@files]);