1) file templates/shaper_helixultimate/features/menu.php
Change all 3 i tags (Font awesome icons) to spans, lines 37, 48 and 56.
You should also add titles to their a tags (anchor links), I suggest you just copy the existing JText::_('HELIX_ULTIMATE_NAVIGATION');
Updated lines now look like this (template version 1.1.4) https://imgur.com/zYNemYP
2) file templates/shaper_helixultimate/index.php
Add a title to the a tag (anchor link) in line 150 once again copying the already existing JText::_('HELIX_ULTIMATE_NAVIGATION');
Updated lines now look like this (template version 1.1.4) https://imgur.com/BuR2jXl
I haven't noticed any layout issues resulting from these changes (template version 1.1.4), they are pretty subtle anyway.
You can check your website's WCAG here => https://achecker.achecks.ca/checker/index.php
I'm hoping these changes will find their way to the next release of Helix Ultimate, making thousands of Joomla websites a little friendlier to people with impaired vision :)