since the java 16 update is released the fps is terrible even when I put the render distance on 2 chunks the fps is still bad.
before java 16 I was playing with 70 to 150 fps but now I'm playing with just 2 to 20 fps

Update: after the 1.17 pre release the fps got better but not as good as before now I'm playing with 15 to 40 FPS and when I enter a cave my FPS goes to 25 to 60 FPS.