Once you inserted favicon but can't see it on your website opened on iOS mobiles. You can fix it by yourself as following solution.
The favicon will show on android mobiles as default, but if you're using iPhone please set it to display favicon as in this guide: http://osxdaily.com/2019/01/28/how-show-website-favicons-safari-ios/
On the iPad, the favicon will be showing properly.
On iPhone, it will not appear on page opening as it's too narrow page space, but it will show on tabs.