Any website that shows which opening a certain player struggles against? Just thought it would be an interesting statistic to know which openings players like Carlsen and Fischer lost most against? Any suggestions?
Opening tree happens to be the website you are looking for, in it you use a database of games or someone's Lichess or chess.com username to get detail about their games. It shows frequency, last played, best win, worst loss, win-loss stats and performance. It also have have fatabases of famous players in it. Checking Anand's games as black, after playing 1.e4 2.c5 3.Nf3 his worst performance is in Sicilian Defense: French Variation (elo performance 2644) with score 107/173 and worsst loss was Ljubojevic - Anand 1998.

Overall, its a nice free website.