Chess engines don’t have real difficulties. Every level of the chess engine is designed to make more blunders as the elo gets smaller.
In other works it is programmed to make bad moves in regular intervals. What that means is even on beginner modes when the engine isn’t blundering it is playing perfect chess. This is why it isn’t good to play against chess bots. At best you will learn some pattern recognition but chess puzzles are better at that.