Yes, on your first character through Legion, you need to do the “hard” version of Uniting the Isles that require rep.
Make sure you’ve done the Legion intro quests and done the quests to get your first artifact and open up your order hall. Without doing that, things can get weird and you might not have access to all of the quests. The order hall scouting map will give you breadcrumbs to start each of the leveling zones. (Suramar starts from Khadgar.)
Here’s a post I made a bit ago with the all the steps and links to relevant quests: