magnus carlsen has played the London
second opening?

The problem with London in this case is not its soundness. It is true that it is probably less played on super GM level, but that is irrelevant for 99.99% of players. It is a playable opening.
There is one other problem in this case. If you play London System, you will generally play the same or almost the same moves every time with white pieces. For someone who plays chess for a long time and is a really a strong player, that itself is not an issue, because he knows other stuff as well.
For a beginner, playing the same type of games every time when you play with white is probably not a great way to play, and additionally it might become tiresome after a while.

The problem with London in this case is not its soundness. It is true that it is probably less played on super GM level, but that is irrelevant for 99.99% of players. It is a playable opening.
There is one other problem in this case. If you play London System, you will generally play the same or almost the same moves every time with white pieces. For someone who plays chess for a long time and is a really a strong player, that itself is not an issue, because he knows other stuff as well.
For a beginner, playing the same type of games every time when you play with white is probably not a great way to play, and additionally it might become tiresome after a while.
Playable, almost all openings are playable. There is a difference between best, better, and good. Superior or Inferior.
In any case, the difference between London System and something with great reputation like for instance Ruy Lopez is pretty much irrelevant on sub 2 000 level, because the difference between +0.3 and +0.1 for the first 10 moves or so, is not something that will decide a game on this level.
The main problem is if someone who just started playing chess plays London System, he will play the same type of positions almost every time with white pieces, which is not ideal improvement wise, as it means that 50% of his games will be similar.
the video I watched on the French defense had the idea of doing f5 to attack the knight defending the pawn .you don't castle or castle queenside
there's no videos on chess.com about the queens gambit