Why is "accepted by Turing Machine with even number of states" a trivial property?
All recognisable languages are recognised by a TM with an even number of states, so the property is trivial.

If a language is recognisable, there is (by definition) a TM that recognises it. If it happens to have an even number of states, then you're done. If it has an odd number of states, add another state that doesn't do anything (or duplicates an existing state), then you have a new TM with an even number of states, and are done.