How do you get Lumin Ambers in Aniimo?

You do not have to hunt for them. An on-screen alert fires whenever a Lumin Amber is nearby, so most of your collecting happens by reacting to a prompt while you are on your way somewhere else. The supply in the open world of Idyll does not run out, which means there is no reason to ration your pickups or save a region for later.

The habit that matters is grabbing them opportunistically while questing. A short detour costs you almost nothing in the moment. Skipping it costs you a return trip across a region you have already finished, and that backtracking is the tedious part of the game. Each amber you pick up also counts toward regional exploration progress, so clearing a region and stocking up on amber are the same job.

The sources worth going out of your way for

Plain exploration is the steady trickle. The larger payouts come from finishing things. Completing or closing a Sanctum rewards Lumin Amber. So does completing an open-world or town trial. Mini games, time trials and open-world puzzles all award it, and quests hand it out as well. If you are short and want a target rather than a wander, trials and Sanctums are the ones to clear.

Why skipping them stalls you

Lumin Ambers are spent to upgrade regional branches and their passive trees, and those upgrades are not cosmetic. Upgrading the Branch unlocks access to new areas. Upgrading regional branches raises your Aniimo capture rates. True flight will not unlock without amber, and the nurturing ability comes from gathering amber and upgrading the Branch. Max the Branch out and you get unlimited stamina outside of combat, flight mode included.

Beyond the Branch, the same resource feeds Pathfinder upgrades, creature progression, equipment, Homeland development and world activities. Bypass it and you are not just behind on numbers. Abilities and whole game modes sit locked behind it.

Not settled: How much amber any single source hands over is not pinned down, so there is no established best place to farm it between exploration pickups, trials and Sanctum clears.