Keys can be a problem because of autorepeat, but here's one that uses the left mouse button for the keyer.

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11112751
use warnings;
use Time::HiRes qw( time );
use Tk;

my $morse = '';
my $text = '';
my $down = 0;
my $lasttime = time;
my $interval = shift // 0.1; # seconds for timing
my $maxlength = 30;

my $mw = new MainWindow;
$mw->geometry('+500+500');
$mw->Label(-text => "Use left mouse button in green window.\n" .
  "Tweek \$interval to your coding speed")->pack;
my $t = $mw->Label(-textvariable => \$morse,
  -width => $maxlength,
  -bg => 'lightgreen',
  -font => 'courierbold 36',
  )->pack;
$mw->Label(-textvariable => \$text,
  -width => $maxlength,
  -font => 'courierbold 36',
  )->pack;
$mw->Button(-text => 'Clear', -command => sub { $morse = $text = '' },
  )->pack;
$mw->Button(-text => 'Exit', -command => sub {$mw->destroy})->pack;
$t->bind('<1>' => \&press );
$t->bind('<ButtonRelease-1>' => \&release );

MainLoop;

sub morse
  {
  $_[0] =~ tr/.-/01/r =~ s/\S+/
    my $pos = oct 'b1' . $&;
    $pos > 30 and $pos = 30;
    substr '__etianmsurwdkgohvf_l_pjbxcyzq?',
    $pos, 1
    /ger =~ s/ *\K //gr;
  }

sub press
  {
  if( time > $lasttime + 6 * $interval )
    {
    $morse .= '  ';
    }
  elsif( time > $lasttime + 2 * $interval )
    {
    $morse .= ' ';
    }
  length $morse > $maxlength and
    substr $morse, 0, length($morse) - $maxlength, '';
  $lasttime = time;
  }

sub release
  {
  if( time < $lasttime + 2 * $interval )
    {
    $morse .= '.';
    }
  else
    {
    $morse .= '-';
    }
  length $morse > $maxlength and
    substr $morse, 0, length($morse) - $maxlength, '';
  $text = morse($morse);
  $lasttime = time;
  }
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