>only play in handheld mode
>never suspend your game

it's literally that simple. suspending the game just totally fucks the performance for me. I always save my game, then close the software. the game runs waaaaay better in handheld mode as well as the lower resolution is easier on the switch. youll still get slowdown in handheld, especially during a weather event or if your battery drains lower than 10%, but it is by and far the best way to play these games