If you use the data pack for the extended height and world generation for the latest snapshot, there can sometimes be massive ore veins generating. In the patch notes, it sai\id there would be large veins, but I don't think they were supposed to be this big.
seed: -1736625532464286500
you have to use the 1.17 datapack for extended height too.
coordinates: 497 -12 -711
put a repeating command block and fly around with this command: command(repeating command block): /execute at @p run fill ~8 ~8 ~8 ~-8 ~-8 ~-8 air replace #minecraft:base_stone_overworld
edit: this might be Works As Intended because a developer posted a picture of this and it was the same size, but I think it shouldn't be this big.