Absolutely nothing is wrong with a4. Stockfish likes it almost as much +2.4 vs +2.5 for dxc6. Yet chess.com instantly labelled it an inaccuracy when I put it in which is lol.
Chess.com pulls nonsense like this and wonders why Lichess gains so many members.
I just analysis the game and the engine says I've made a brilliant move, what is it?
I don't see the difference between best and brilliant move in that game [and others].
The game's here