1.16.5 Glitched Out

When I loaded into my Minecraft world I had to update it from 20w51a to 1.16.5, So what happened was when I loaded all the entities disappeared our pets and everything, also copper didn't exist at all...and I didn't make a backup because it always works when updating but when I updated there was some really dark stuff, that is because those spots were copper ore or copper and now we have to get new pets an everything....