Guide
The Amber Ardenmoth mount has a low chance of being inside the Wild Hunt Supplies. These are rewarded once you reach Exalted with the Wild Hunt and then every 10k reputation past Exalted will award you with Supplies. This reputation and mount can be gained by any covenant.
The reputation is gained by firstly via completing the yellow quests within the zone and then from there your main sources of reputation will be World Quests and Callings tied to Ardenweald. Callings are essentially the new version of Emissaries from Legion/BFA.
You can also pick up a Wild Hunt Contract that will give you an additional 10 reputation per World Quest you complete, regardless of which Shadowlands zone it is in.
Repeat this daily content until you reached Exalted and then work towards Supplies every 10k reputation.