The Petrov or Russian opening is seldom seen these days:
[fen ""] 1. e4 e5 2. Nf3 Nf6
Why? Is it fully refuted? Or merely uncomfortable for Black?
There is nothing wrong with the Petroff and it is still used regularly at the highest levels. If it is less popular than it used to be (and I'd have to check the data before claiming that), then that would likely be because it is usually played when Black is trying to make a draw, and these days the Berlin variation of the Ruy Lopez is the most popular way to try to achieve a draw against 1.e4.
What's "wrong" with the Petroff is that it is "boring," and associated with playing to draw, because it is somewhat symmetrical.
Most people, even Black, like to play to win, and when they do, their choice is "sharper" Sicilian, or French, or even certain variations of the Ruy.
I remember people using it in my high school days (forty years ago) when they were ahead in the tournament, and just wanted to finish with a good score.
I wouldn't call any of those moves wrong, but I would say it is a bad idea for Black to move
2. ... Nf6.
If you are an optimistic player who thinks that White and Black are even at first glance, my Houdini counters by saying White is already one point ahead.
In one classical game, it goes like this:
C42 Russian Game: Classical
[FEN ""] 1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3 Nxe4 5. d4 Be7 6. Bd3 f5