Here is how to activate PPL(Single Tap Highlight Ext - PPL), which is different for iPhone, iPad and Mac.
1. iPhone, iPad
(1) Press the setting icon
(2) Select Safari
(3) Select Extensions
(4) Select PPL
(5) Set to the state shown in the image. PPL is now enabled. The next step is to operate it.
(1) Launch Safari and select Preferences from the top left menu.
(2) Select the Extensions tab and set it to the state shown below. Now you can use PPL. The next step is to operate it.