The array you populate in serial_finder() is private to that sub:

sub serial_finder {
    my @list;
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The array you attempt to populate the edit field from is declared at the top of the program:

my $comport = 1;
my @list;
...


sub com_list_create {
    print "running\n";
    foreach my $comlist (@list) {
...
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Two different lists! The first is thrown away when you exit the sub because you never return it anywhere. You could just drop the my on the first one and they would then both use the same list and things would probably work.