Your templates have a maximum-scale=1 in viewport:
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1"/>
I have customers they don't want this because they say there are many visitors that
- are (older) people whos eyes are not that good anymore
- People of any age with visual impairment
They will not be able to zoom in.
I can remove/change maximum-scale=1 in file inc/style.php but will lose it on next template update.
Maybe you want to consider to remove maximum-scale or at least set it to a higher level, lets say maximum-scale=5 ?
Just a thought... :-)
Patrick