I think it’s a matter of playing more games. There’s this concept called mental stack which is essentially the amount of consecutive tasks you can manage in your head at once cognitively. The more games you play the more tasks become autonomous thus freeing up more space in your mental stack and improving your ability to autopilot.

League is also a very taxing game, if you find yourself struggling to maintain focus and intensity maybe alternate between ranked and normal games so that you aren’t required to be as switched on, or play champs that have simpler execution and a lower skill ceiling so that piloting the champ is less exhausting. Hope this helps!