The Outriders demo might be limited in scope, but you can play it as much as you like, which means there is some farming potential there. The World Tier dictates all loot drops, and the highest World Tier you can reach in the demo is World Tier 5.
The good news is that there is a way to keep replaying content so that the main loot chests can be farmed, even though after you finish a quest of part of the story, the chest is effectively empty.
When loading up the game, the main screen will show a button on the left that says “Select Story Point”. This allows players to get back to just after the tutorial and start all over again, but keep their progress. All levels, skills, and gear collected so far will remain, including any unlocked World Tiers, but players can start the story all over again.
This means you can play through all the missions and side quests, opening all the loot chests at a higher world level with a greater chance of dropping a Legendary. When the story is finished, you can then rinse and repeat the process.
Loot and gear will carry forward from the demo into the official release, so this farming method is actually worth doing to be as prepared as possible for the full game when it launches.