Is "to be interested" an active or passive voice?

The verb interest has the following obligatorily transitive senses [Collins CoBuild Dictionary; modified]:

interest (3) verb

If something interests you, it attracts your attention so that you want to learn or hear more about it or continue doing it.

Animation had always interested me. [S + verb + DO, noun/pronoun]

[This passivises, to say The horse is always interested by people walking along the road.

But there needs to be a by-phrase to show a verbal usage;

*/?? He was interested in sports by ... (and this sounds unidiomatic; see below)]

...

......................

interest (3) verb

If you are trying to persuade someone to buy or do something, you can say that you are trying to interest them in it.

In the meantime I can't interest you in a new car, I suppose? [S + verb + noun/pronoun + in-phrase]

[But this has a restricted distribution, and certainly resists passivisation

I was interested by him in a new car (nigh on unacceptable; we'd say 'He got me interested in [buying] a new car.)

.....

He interested me in sports. [borderline acceptable; present tense worse]

.....

I was interested in sports by him. [borderline acceptable; present tense worse]

......................

So 'I am interested in sports' is best regarded as a copula + adjectival complement

I am interested in sports. ......... compare

I am happy with my old car.