shouldnt this be after the if and not before

Also it would be better to only have class=hidden and then create an override for beez

1. I think not. In fact there is no problem if the header elements start with <h2> or with <h3>. The problem is the sequence <h1> -> <h3>. So the workaround is needed only when page_heading, <h1>, is displayed.

2. Ok. Tks.

either i completely misunderstand this code or your new code is h2 when it should be h1

<h3> elements are always present: they are tagged items.

When Page_heading <h1> is set to be displayed, this PR assures it is followed by a hidden <h2>, even if menuitem param says not to display the tag_name, <h2>.

When Page_heading <h1> is not displayed there is no need for this PR workaround, in fact:

• if tag_name <h2> is set to be displayed then the sequence will be <h2> -> <h3>;
• if tag_name <h2> is set not to be displayed the sequence will begin with <h3>.

In bothe cases the sequence is ok; in fact it is a11y valid if the sequence begins with <h2> or with <h3>.

Said in other words, the code does what's needed to have one of these valid sequences:

1. <h1> (page_heading) -> <h2> hidden (tag name) -> <h3> (tagged items)
2. <h1> (page_heading) -> <h2> (tag name) -> <h3> (tagged items)
3. <h2> (tag name) -> <h3> (tagged items)
4. <h3> (tagged items)

This covers all the permutations of the two options involved.

All the section can be rewritten using an additional variable, this way:

<?php if ($this->params->get('show_page_heading')) : ?>
	<h1>
		<?php echo $this->escape($this->params->get('page_heading')); ?>
	</h1>
<?php endif; ?>
<?php $a11y_hide_h2_fix = ( $this->params->get('show_page_heading') && !($this->params->get('show_tag_title', 1)) ) ? ' class="hidden"' : ''; ?>
<h2 <?php echo $a11y_hide_h2_fix; ?> >
	<?php echo JHtml::_('content.prepare', $this->tags_title, '', 'com_tag.tag'); ?>
</h2>

For beez3, is it better to:

1. add the .hidden {display: none; visibility: hidden; } class to templates\beez3\css\layout.css or
2. make a view override, just to replace the hidden class attribute with unseen?

I'd prefer 1.

I tested it in J! 3.7.4 / 3.7.5 and 3.8beta. It's working.
Did someone else test it?

@LivioCavallo can you please give exact Test Instructions in your first Comment?

@franz-wohlkoenig I gave detailed test instructions; are them ok now?

Sorry that it took so long to respond. Can you please check if the problem is still present in Joomla 4 and rebase the PR to the 4.2-dev branch? In the meantime I'm closing the pr, when ready please reopen so we can properly test it. Thanks for your contribution, making Joomla better.