Dragonflight does not include Threads of Fate, but we’ve got some details on how alt leveling works in the new expansion.

Leveling Your Main Character

Leveling up the first character is linear, and you must complete the zones in the following order:

The Waking Shores > Ohn’ahran Plains > The Azure Span > Thaldraszus.

Leveling Your Alts

When you complete the Dragonflight campaign on your main character, you can pick any of the four Dragon Isles zones for leveling and you will have World Quests and Side Quests unlocked on your alts.

Thanks to MrGM for the screenshots.