Do you play your games more quickly or do you take time to think things through? 🎯
Here's the thing: playing against the computer is brutally honest, but not necessarily the best training to reduce tactical mistakes. Engines see five moves ahead, you maybe see two - that's unfair. Better to play against people at your level first (also on lichess, in blitz or rapid), because they make similar mistakes as you do and you can learn from their thought patterns. You only beat the engine if you take your time and actually calculate every move like it does - that's exhausting and doesn't really change your fundamental understanding of the game.
For the tactical forks: do tactical puzzles regularly on the side (also on lichess in the training section). That trains your pattern recognition - after a while you'll spot forks and skewers much faster intuitively. 15 minutes a day is enough to improve. And if you want to play against the engine, set it to a level where you realistically win 30-40% of the time, not "medium", where it just frustrates you. 💪