Two Act 1 roads
The Underdark and the Mountain Pass are both Act 1 routes. The notes do not put them in a required order.
The grove resolver is the popup on the way out, the same warning as the Act 1 softlock page.
The time-sensitive list names the road to the Rosymorn Monastery Trail and the road into the Shadow-Cursed Lands as popups that auto-resolve unfinished business. Save the Refugees ends if you take either Act 1 exit.
Halsin dies in his cell if those exits are taken before he is freed. Karlach leaves if the paladins of Tyr from Hunt the Devil are still alive when you take them.
Mountain Pass
The mountain exit is the road to the Rosymorn Monastery Trail. That is the name on the Act 1 page. Lae'zel's crèche is the stop that trail is known for.
After you approach Waukeen's Rest, entering the Rosymorn Monastery Trail kills the trapped survivors, including Benryn. A long rest or a fast travel does the same.
Underdark and Grymforge
The Underdark is the other Act 1 road. It leads to Grymforge. Nere's clock starts only after you speak to him through the rubble there.
After you speak to Nere through the rubble in Grymforge, he dies if you long rest twice, leave the region twice, or mix those two. The gnomes tied to Save the Grymforge Gnomes disappear on the same clock.
Official site: baldursgate3.game.