House

In the modern era, some Muslims have become very sensitive to the question of shirk by considering any number of physical objects to be shirk. This includes sacred objects, shrines, etc.

(This idea primarily comes from Wahhabism and Salafism, but some other Muslims have taken it on board too.)

Similarly, Wahhabism and Salafism reject most forms of intercession as shirk, whereas many Muslims before that accepted the idea of intercession.

The Qur'an itself does not state that the notion of sacred objects is shirk. Rather, shirk is when you directly worship beings other than Allah.

So, keeping an alam, in and of itself, is not shirk.

Possibly, some views are cultural. Since alams are most common historically in Iran and the Indian Subcontinent, it has been more common for Shia in other regions, where alams were not common, to criticize the practice. (That is, it was seen as being culturally different and hence suspicious - man is an enemy of what he does not know.)

On the flip side, some Muslims in the Subcontinent have felt cautious about the cultural influence of Hinduism, and so for this reason try to avoid physical objects in devotional practices. (We tend to be most cautious about the things we are closest to, which might be seen as a competitor.) Although I think this is less common.

It is mentioned in La'ali al-Akhbar (vol 3, p 413) and attributed to Imam al-Baqir (A) that the angel Jibra'il told the Prophet (S) that the planet Venus (the evening star) would descend on Friday night on the house of the person whom Fatima (A) should marry. The people waited to see who it was, and it was the house of Ali (A).

This narration is provided as part of the explanation of the origins of the tasbih of Fatima al-Zahra (A).

I am personally not aware of any chain of narration for this and therefore, without a chain of narration, it would not be classified as authentic.

Allah knows best.