broken chunks no matter what I do

My minecraft world has been corupted and I don't know how to fix it. This has happend before in the 1.16 snapshots and in 1.13. I looked it up and I saw many fixes online but none of them worked. On the border of where chunks are supposed to be there are none and I can't place blocks there and on the border of the few existing chunks the blocks are darker. I used the commands /setblock,/fill,/reload and /debug and it wouldn't work. It fixes after like 30 minutes of waiting it loads but my fps is at the highest 3.