We can only envision intelligent aliens with an advanced civilization taking on a humanoid form, because that's all we know.

However, our form is a consecuence of having evolved from apes, a series of long coincidences which first saw us evolve brachiation and opposable thumbs to climb and swing from trees (monke stage), then saw us climb back down and lose our tails as we adapted again to the ground (ape stage), and finally adopt bipedalism as we moved into the Savannah (hominini stage).

It's very unlikely this set of coincidences will repeat in the evolution of an alien species.

What other shapes could intelligent life take? They would need access to fire to develop metallurgy, and some kind of appendage to manipulate its environment.