Originally Posted by hokiefyd

Note that all bike manufacturers' websites state that components can change at any time and without prior notification. It's very likely that, due to the tremendous supply chain disruption over the past year, Trek had to use the nearly identical Acera rather than the Alivio that the original spec sheet may indicate. The bike will operate just the same regardless, mechanically. You should not notice any operational difference between these two derailleurs, assuming both are adjusted and indexed correctly. There are styling and very small material differences but they are otherwise functionally the same.

If you're stuck on the principle of the matter, beyond Trek's disclaimer that parts can change without notice, then perhaps you can get some credit back from them on it. I think there was a recent case where Trek was using a lower-spec tire on a bike and some folks here complained and Trek sent them some new tires.