I found a phenomenon, the version is 1.17.1, when you press F1 to close the game GUI, FPS will increase a lot. But when you open the game GUI again, FPS will decrease. On my older computer equipment, it will be reduced by 20-40FPS, if you press F3 to check the FPS, it will be more obvious (I think it is because there are too many texts)
In other words, if you press F1 without the inventory GUI below, it will be smoother