What is the difference between karpov caro kann and fort knox french?

Few things are different. But essentially it's a caro kann structure. The only thing is the soundness. It loses a few tempi.

I am no expert in these positions but a few points

1. A difference of 0.3 in evaluation is very minor. Don't make to much out of it
2. If I look at the position the main difference is that in position 2 black has (due to the fact that the bishop on g4 pins the knight) a little pressure on d4. Pressure cannot really be naturalized without making some small concession
   1. He can play h3/g4 but this weakens the kingside
   2. He van play c3 but than he cannot push c4 anymore and probably every plan what has in this position involves expansion on the queenside
   3. He can play Be2 but this costs a tempo and the white bishop is passive on e2

The differences are very minor but so is the difference in evaluation

They are not literally the same thing.

One still has the light-squared Bishops on the board, the other doesn't.

If we were to magically remove the bishops Bd3 and Bg4 in the Karpov, then both positions are the same, except that in the Fort Knox white has the move and has already played Re1, while in the Karpov white has the move and has not yet played Re1. So the difference is 1 tempo = 1/3 pawn = 0.33.

it is the same pawn structure so many of the ideas in the position will be shared, however there is a key difference in the position, and that is the light squared bishops.

as for why there is a different evaluation for such a similar position you can attribute it to the bishops having different values. The bishop on g4 is quite annoying for white as it exerts a pin and it is difficult to remove without weaknenign the kingside with h3, g4 or wasting a tempo on a move like Be2, Ne5. compare this to white's light squared bishop where it sees nothing on the board and has very few prospects. It does add pressure to the kingside so black has to be a little careful with castling, but yet again his light squared bishop will save the day by either retreating to g6, or trading on f3 where white will not have enough material to mate black.

compare it to this position which rests at 0.57-0.62. you'll see the same pawn structure but the light squared bishop is stuck behind the pawns. this gives white an advantage because now the light squared bishop is not really contested on the kingside and castling can be quite dangerous for black.

Another reason why the fort knox has a high evaluation is because of the activity. white's pieces are positioned well and can quickly play for Bg5, c4, d5 and black will have to play really accurately to equalize.