Learn Portuguese (Portugal): O elevador está avariado.

We use the verb estar because a broken elevator is a temporary state or condition. Once it gets fixed, it will work again. If you used ser (é), it would imply the elevator's permanent, defining characteristic is being broken!

I usually use partido for broken. Why is it avariado here?

In Portuguese, the word you use for broken depends on what is broken. Avariado is used specifically for machines, appliances, and mechanical systems that are malfunctioning or out of order. You use partido when something is physically snapped, cracked, or shattered, like a window or a bone.

Does the ending of avariado change depending on the object?

Yes! Even though it comes from the verb avariar (to break down), it acts as an adjective here describing the elevator. Because elevador is a masculine, singular noun, it ends in -o. If you were talking about a broken washing machine (a máquina), it would change to avariada.