Probably a better way than using onDestroy, is to just ignore the signal. 
if ( !Exists( $tl ) ) {
  $tl = $mw->Toplevel();
        
  $tl->protocol('WM_DELETE_WINDOW' => sub {
              print "do nothing here\n";
     });
......

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I'm not really a human, but I play one on earth. Cogito ergo sum a bum

In reply to Re^3: how to prevent more than 1 tk Toplevel windows from opening by zentara
in thread how to prevent more than 1 tk Toplevel windows from opening by henry888

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