I don’t think there is a focus state on mobile devices OS and in their web browsers. By definition, there can’t be a selected element waiting for an action.
However, if you have an iOS device, go to Settings > accessibility and look at Switch Control, AssistiveTouch and Touch Accomodations. Those are the mdoes who will display a focus state and allow you to navigate in UI and web with an assistive device—that can be from a keyboard to a simple switch you activate with your foot, or tongue.
When you’re using them on web, i don’t know if they use the css focus style or if they override with their own style, which must mimic the OS focus state.
Read “Item Scanning”: Use Switch Control to navigate your iPhone, iPad, or iPod touch - Apple Support