I'm posting this because this year some very interesting games have been played showing new ideas just discovered for White which can give an idea of how difficult it is to prepare especially at the very top level.
The first game that I want to mention is the game between Ivanchuk and Wesley So played this year in Wijk aan Zee. So played a new line (well known to the top players thanks to an article published by Anish Giri in New in Chess). Ivanchuk didn't know the line and got crushed. You can see an analysis of the game by the GM Jan Gustafsson here.
The second one is one played in the final of the World Cup in Baku between Peter Svidler and Sergey Karjakin which also displayed a very interesting line. It was a blitz game where Svidler got a huge advantage thanks to his better preparation but finally lost due to blundering a rook.
To sum up, if you're interested I recommend you the series of videos made by Jan Gustafsson for Chess 24 called Latest Trends on the Marshall where you can find some very interesting ideas for both Black and White like the two mentioned above.