It's easy once you understand the system.
Index → https://8ch.net/qresearch/index.html
What you see there scrolling down is like Trail Heads to various threads.
So, just scroll down until you see
Welcome To Q Research General
Right ABOVE that red line, you see
→ the bread number #XXXX and title, AND
→ these buttons [Reply][Watch Thread][Show All Posts]
Clicking on [Reply] takes you right inside the current thread.