This is all subjective of course, but the thread is asking for my opinion so here it is.
I think there is a difference between a retro game and a game made in a retro style.
This thread is blurring the two.
Lots of newer indy games are made in the retro style. I just played Gigasword which was a fun Metroidvania/Puzzle game in this style.
But the "newest" game that I'd consider retro is anything from Gen 6 (PS2/GC/Xbox).
After that generation, we started getting wider use of Bluetooth, HDMI, and motion controls which really changed things in a way that I personally use to delineate retro/modern.