My advice is to not touch it. Ttip text requires javascriot you are not
including as far as I can see. This will cause bc breaks in front-end. Not
on computer, reading code on phone. Please Don't touch it.

Maybe we just have to add JHtml::_('bootstrap.tooltip'); ?

My eclipse (Keppler) is real unhappy about each of these files and mark them with a red cross.

or, my eclipse would be satisfied with:
title="<?php echo '<strong>' . JText::_('COM_USERS_USER_FIELD_TWOFACTOR_LABEL') . '</strong><br />' . JText::_('COM_USERS_USER_FIELD_TWOFACTOR_DESC'); ?>">
instead of the existing
title="<strong><?php echo JText::_('COM_USERS_USER_FIELD_TWOFACTOR_LABEL') ?></strong><br /><?php echo JText::_('COM_USERS_USER_FIELD_TWOFACTOR_DESC') ?>">

test ok on 50% here
in backend all good, but on the site I got:

not very understand why, because strings looks the same

and small wish, can you please use JHtml::_('tooltipText', 'string1', 'string2'); instead of JHtml::tooltipText( 'string1', 'string2'); ...
so people who override core JHtml::tooltipText method, can be sure that it work as expected everywhere

This is why I proposed the second solution:
title="<?php echo '<strong>' . JText::_('COM_USERS_USER_FIELD_TWOFACTOR_LABEL') . '</strong><br />' . JText::_('COM_USERS_USER_FIELD_TWOFACTOR_DESC'); ?>">
so that we do not mess with js.

BTW: my screenshot above was in frontend.

not sure, I tried couple times, but string still untranslated, very strange...

JHtml::_('bootstrap.tooltip') already loaded in the label layout layouts/joomla/form/renderlabel.php, when Joomla render other fields ...
and I see no problem with use JHtml here, as the label already has class class="hasTooltip", so tooltip script applies for this label, even without this patch

the strings were wrong for frontend in this patch ;)
I am correcting this now and follow @nikosdion advice to not use JHtml::tooltipText

I change the PR to use the alternative code to, at least, make Eclipse happy.

Please test again

test works good

@zero-24
Can you test and RTC as it is a very simple change?

Works & Nothing is broken. --> RTC Thanks.