Why are you relying on open to determine your type? -f works just fine on expressions, a.k.a. paths in strings.

#!/usr/bin/perl -w
use latest;
use File::Spec;
my $test=$ARGV[0];
sub bfs
{
    my $path=$_[0];
    push(my @queue,$path);
    my @output;
    while(@queue)
    {
        $path=shift(@queue);
        if (-d $path) {
            my $dirname = (File::Spec->splitdir($path))[-1]; # Grab th
+e last entry
            next if $dirname =~ /^\.\.?$/; # . or ..
            opendir my $dh,$path or die "opendir failure, $path: $!";
            push @queue,map {File::Spec->catfile($path,$_)} readdir $d
+h;
        } elsif (-f $path) {
            say $path;
        } else {
            # say "Other entity encountered: $path";
            next
        }
    }
    return @output;
}
bfs($test);
[download]

Note I've removed the open on the files entirely, and scoped the directory handle appropriately so that Perl closes it as the variable goes out of scope. I've also used File::Spec's splitdir method to make the directory name check actually cross-platform (as long as you'd started down that path...).