I believe I know one area you were talking about but I am not certain of the second. Removing all the comments, is this what you mean?

if ( defined $default ) {
    my $stderr;
    close STDERR;
    open(STDERR, ">", \$stderr);

    my $grabkey_thread = threads->create(\&grabkey);
    $grabkey_thread->detach();

    for ( my $i = 0; $i <= $timeout; $i++ ) {
        sleep 1;
    }
    
    my $pos = index( uc( $choices ), uc( $default ) ) + 1;
    print uc( $default ) . "\n";
    exit $pos;
    
} else {
    grabkey();
}

=>

if ( defined $default ) {

    my $stderr;
    close STDERR;
    open(STDERR, ">", \$stderr);
    
    my $grabkey_thread = threads->create(\&grabkey);
    $grabkey_thread->detach();

    for ( my $i = 0; $i <= $timeout; $i++ ) {
        sleep 1;
    }
    
    my $pos = index( uc( $choices ), uc( $default ) ) + 1;
    print uc( $default ) . "\n";
    exit $pos;
    
}

grabkey();
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