my @looper = (0..5);
	
foreach my $lp (@looper){
	... subprocess preparation as in the OP ...
	sub {
		my $i = $lp || 5;
		return $i;
	}
}

##</code><code>##

use Mojo::Base -strict, -signatures, -async_await;
use Mojo::IOLoop::Subprocess;
use Mojo::Promise;

async sub testMehod{

    $c->render_later;
    my $start_timer1 = Time::HiRes::gettimeofday();

    show "BEFORE";

    my @promises;
    
    my @looper = (0..5);
    
    foreach my $lp (@looper){

        say "(START) This is $lp loop";
        
        my $subprocess = Mojo::IOLoop::Subprocess->new;
            
            push @promises, $subprocess->run_p(
            
                sub {
                    my $i = $lp || 5;
                    my $sp = shift; # $subprocess
                    #my $i = shift || 3;
                    #my $promise = Mojo::Promise->new;
                    
                    say "Hello, from $i and $$!";
                    sleep 2;
                    say "Good bye, from $i and $$!";
                    
                    #$promise->resolve("Done for $i");
                    #return $promise;
                    return "Done for $i";
                #}->($_)
                }
            )->then(sub ($_result) {
                show $_result;
                return $_result;
            })->catch(sub  {
                my $err = shift;
                say "Subprocess error: $err";
            });
        $subprocess->ioloop->start unless $subprocess->ioloop->is_running;
        say "(END) This is $lp loop";
    }


    my @results = await Mojo::Promise->all_settled(@promises); 
    show @results;

    my $stop_timer1 = Time::HiRes::gettimeofday();
    my $total1 = sprintf("%.5f\n", $stop_timer1 - $start_timer1);

    return $c->render(text => "All done. Parallel: within $total1", status => 405);
}