How do you unlock worker automation?

The gate is the Homeland RV, not a character level, a story beat or a creature you have to catch first. That means automation is bought with base progression, and it sits at the very first upgrade step rather than somewhere deep in the RV track. If you are planning what to spend early Homeland resources on, this is the cheapest point at which the RV starts paying you back.

Before that upgrade, none of your Aniimo will work on their own. So the practical advice is to push the RV to level 2 as an early priority and treat other Homeland spending as something that can wait behind it.

Unlocks the RV does not cover

Raising the RV does not carry the region systems with it. Weather control is tied to a region's bloom branch instead: upgrade the branch and you gain the ability to change the weather, with Prismana weather control opening at 60 percent completion of the bloom graph. Nurturing a region is its own gate again, and it costs 30 Lumin Amber submitted at the branch.

Two more unlocks in this stretch of the game come from combat and crafting rather than from any base track. Defeating Alpha bosses drops loot and opens evolutionary paths for specific Aniimo, so an evolution you are missing may be sitting behind a boss rather than behind a building. Crafting a legendary Anipod unlocks the encounter to battle Erissalis, also written as Irisalis.

Not settled: What later RV levels add to automation, and how much of the Homeland your workers will cover once it is running, is not settled yet.