use strict;
use warnings;
use Tk;
my $msg ='MainWindow'->new->messageBox(
        -icon    => 'info',
        -title   => 'MSG',
        -message => '| | | | | | | | | | | | | | | | | | | | | | | | |
+ | | | | | | | | | | | |',
    );
MainLoop();
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leads to this window. Is the problem you mention present in the picture?