If worse comes to worse, you can always setup a timer, that runs for the duration of the ProgressBar, in the sub for the timer, just do $toplevel->raise. It will keep making the toplevel come to the top. You might also be able to do it in your ProgressBar loop. Or check out this:

#!/usr/bin/perl
#$top->deiconfiy; 
#$top->raise; 

use Tk;
$mw = tkinit;
$t = $mw->Toplevel;
$t->withdraw;
$t->Label(-text => "Testing...")->pack;
$t->Button(
   -text => "Withdraw",
   -command => sub {$t->withdraw},
)->pack;
$t ->overrideredirect(1); #to top on all virtual desktops 

$mw->Button(
   -text => 'Test',
   -command => sub {
       $_->deiconify, $_->raise for $t;
   },
)->pack;

MainLoop;
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