Linking verb's complements

Hello everyone. I hope you all to have a good day.

In many English grammar websites, I read that prepositional phrases, adjectives cannot be complements of verbs.

I am not sure whether they are talking about active verbs or not but if they are talking in general, I think that there is something wrong there. Let me explain you why.

1-) I was at the party.

What is the function of "at the party" here? It is meaningly a subject complement but I am not asking it as you probably guess. Its function is like an adverbial prepositional phrase saying where I was and I think that "At the party" is theoretically the complement of the verb "was".

2-) I was happy.

What is the function of "happy" here? Again It is meaningly a subject complement but the adjective "happy" seems to be the complement of the verb "was".

3-) I am considered to be a smart person.

The same question here. According to me,

"A smart person" is the complement of the verb "be".

"To be a smart person" is the complement of the verb "considered".

"Am" is the auxiliary verb here.

What do you think? Where am I wrong? Thanks..