Does a Will-O'-Wisp need to use the hide action after turning invisible to be hidden?

Question

This question's solution says that as long as any part of the creature or clothing its wearing makes a noise it can be detected. A Will-O'-Wisp is ephemeral, has Incorporeal Movement,and flies. With all this going for it a Will-O'-Wisp should be undetectable while invisible without needing to hide unless, it has a smell/scent, Incorporeal Movement leaves a detectable trace in the air,it or its movement makes noise.

Players Handbook PG 177, Hiding says "An invisible creature can't be seen, so it can always try to hide." which indicates to me that unless an ability explicitly says you become hidden that you're always detectable in some way outside of your control.

I feel like I've come to the correct conclusion but would like confirmation or an explanation if i'm wrong.

Answer 1

Strict RAW is that it still must take the Hide action

Because the Will-o'-wisp (MM, 355) doesn't say it automatically Hides, then it simply doesn't and while it can turn invisible as an action, it also still needs to Hide.

While your logic around it being ephemeral makes some sense, the mechanics of ephemeral only state:

The will-o'-wisp can't wear or carry anything

and the mechanics of incorporeal movement only state:

The will-o'-wisp can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

There is nothing in the stat block that suggests those mechanics do more.

Of course, a DM may alter it to auto-hide, but otherwise it's the default of the creature's location is known, but attacks against it would have disadvantage (and it can't be targeted by anything that requires sight.)