If you want to enable pinch to zoom om mobile, you need to place this code in Theme Options -> Integration -> Add code to the < head > of your blog:
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=2.0, user-scalable=1" />
In the picture above, the Divi theme is used but that code will work for any theme, for the ones which don't have Theme Options, you can place the code directly into the header tag of the theme in /themes/theme-name/header.php right before the closing </head> tag.
Make sure to use a child theme, so the changes are not deleted after a theme update if you are placing it into the header.php file.
The depth of the zoom can be controlled from this part:
For a deeper zoom, change the value to 2.5, 3.0, etc.