I use this button when clicking the thread doesn't lead to first unread post (happens when I haven't visited the thread for a long time). But it's not available in the mobile site. Can that be changed please? Thanks.
What's missing exactly? Do you mean the leading dot in front of thread titles? The image attached is from an Android phone, when logged into my account. (Note - dots don't appear if not logged in.) I checked iPhone, and it had the dots, too.
That "Go to First Unread" link simply is set to disappear when the small width phone-sized view is used. The smaller screen requires some things to not be displayed. That happens to be one of the things that is dropped. I've checked all the styles, and they all do it. It's not a setting I set or control.