I have no preferences chosen to separate read from unread. I see the complete thread index, threads from initial post to latest post, whether I've read them or not.
On my Android and Windows devices, if a thread is new, or if it has new replies since my last visit, the thread title is in bold font. If I've read the thread and there are no new posts since my latest visit, the title is in normal font. This way I know I'm never missing anything.