Invoke tagConfigure with the -state parameter, with a value 'hidden'. When this tag is added to a range, the text will not be displayed in the text widget. Invoking tagRemove with the tag name and range will make the text visible again.

# A quick demo: hide the selected text,
# press the Escape key to make hidden
# text visible again

$mw = tkinit;
$t = $mw->Text->pack;
$t->tagConfigure(
    'hide',
    -state => 'hidden',
);
$b = $mw->Button(
    -text    => 'Hide',
    -command => \&hide_text,
)->pack;
$mw->bind('<Escape>', \&show_text);

MainLoop;

sub show_text {
    my @r = $t->tagRanges('hide');
    return unless @r;
    $t->tagRemove('hide', @r);
    return;
}

sub hide_text {
    my @r = $t->tagRanges('sel');
    return unless @r;
    $t->tagAdd('hide',@r);
    return;
}
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