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.
Nah last few years have released some of the best games of all time. Just this year alone we got TOTK and Baulders Gate 3. Gaming is in really good shape right now.
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.