Not much? I eyeball it as about 1/4 of the games being in the last two years. That seems pretty reasonable to me.
If an actual majority were brand new games it would just tell you that PC gamers (or at least steam deck) are just chasing novelty over quality. It's OK not to play every brand new game right on release, and it's OK to play older games.
I think it says far more about the capabilities of the steam deck. The thing is perfect for older, less intensive titles. I wouldn't expect this list to be filled with new releases.