Game FPS drops or even freezes every few seconds on Mac

I just got a new Mac, and I tried to play league of legends on it, but this frustrating problem really annoys me. During the game, the FPS will suddenly drops to 06 - 09, which makes you to loss all the tracks of the current situation, and you can walk into random places, get shot by whatever abilities, and die miserably without knowing why cuz you basically loss control of your game. It happens about every 10 seconds, and it creates a horrible experience throughout the entire gameplay. Riot, you really need to fix this. I just did some researches and I saw posts from several years ago complaining the exact same question which means you guys did not fix this bug for all these years. Come on. This Mac works perfectly fine for other games, and I do not know what is wrong with this.