I'd like to run another program from my script. Both programs have a Tk interface.

There is your problem. What should have been a Tk::Dialog you've turned into another app.

Anyway, it works for me, and focusForce overrides the blinking taskbar behaviour on win32 (which I'm fond of, since I don't like apps to steal the focus from me)

#!/usr/bin/perl --
use strict; use warnings;
use Tk;

my $mw = tkinit();

$mw->Button(
    -text =>  'go' ,
    -command => sub {
        $mw->Busy;
        $mw->iconify;
        $mw->withdraw;
        
        system $^X, '-MTk', '-e', 'tkinit;MainLoop' ;
        
        $mw->raise;
        $mw->deiconify;
        $mw->update;
        $mw->focus;
        $mw->Unbusy;
        $mw->focus;
        $mw->focusForce; # win32
        
        return;
    },
)->pack;

MainLoop();
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