I was playing a game where I conquered some systems from the Cravers, and those systems contained depleted planets. I wanted to restore them so I sent over a Behemoth with a couple of restoration modules that "remove depletion points each turn".

However, when I parked my Behemoth on my depleted system, there was no button I could click to tell it to restore the planets:

As you can see in this picture, I can't click the "Restore planet" button as I already own the system, and apparently this is a Behemoth action I can only do on empty or other empires' systems. This is a bit confusing, seeing as I'm pretty sure you can perform the other Behemoth actions (terraform and reduce anomaly) when orbiting your own systems.

But I then found that my Behemoth was in fact removing depletion points! When I looked at the system management, it showed that depletion points were going down:

Many turns later, you can see my depletion points are greatly reduced:

This is just not clearly visible on the galaxy map. Looking at my Behemoth orbiting the system (and being unable to click the "Restore planet" button) seems to indicate nothing is happening, yet in fact the depletion points are being removed somewhat secretively.

When you tell a Behemoth to terraform a planet, there is a visual on the galaxy map, where you can see the Behmoth spreading Dust onto the system. The Behemoth's tooltip also gives you information about the terraformation, i.e. turns to complete. I think it would be good if there was something similar for restoring depleted planets. Maybe instead of making it completely passive, have it so that the player has to click that Restore planet button, so that they know for certain they are fixing their depleted planets. The Behemoth tooltip could then list some information that you can see on the galaxy map.

Further, on the system management view, it would probably be helpful to list the factors affecting a planet's depletion points, as things get complicated when you're trying to restore a planet that has Craver populations sitting on it. Perhaps something like:

Depletion Points: -1 per turn

+3 from population

-4 from Behemoth modules

I do worry about how unclear this game can be regarding some mechanics.

(Can't really post this in the Bug Reports forum as I think everything is behaving as intended, but the mechanics are just unclear and I hope the devs will have a look at presenting it better.)

Although I agree, that this looks confusing, it is still in coherence with how all other mechanics work. Action button is there to restore depletion points on non-colonized systems (cravers left or Hissho used Core miner).

Still, passive kick in on your own systems automatically, because it would be tedios to reapply restoration every turn once it is fully restored, if there is still source of depletion present.

AFAIK restoring depleted planets is a passive skill. IIRC the only passive skill regarding terraforming/restoration/...