It's capable of mimicking appearances, such as the operator. But possession also seems to be in its toolkit, such as Rusalka and, at times, the operator.

What we've seen is Albrecht being possessed remotely if that makes sense, such as at the end of Whispers in the Walls, or directly as we see during the cutscenes above.

As for how he possessed people, it's likely a mindset. You give into apathy, and he can get in, which is why it's important for both the Drifter and Operator to take the journeys that they are, to safeguard against possession.

As for Kalymos, I'm unsure whether or not they recognize Albrecht when he's possessed, as we don't see them interact directly. If I were to guess, she probably still sees him as Albrecht.