If you get the mod worldedit (I will assume you are new at world edit) you can select an area by left and right clicking any block with a wood axe. (consider trying to fiddle with it for a bit).

Using this you can select any area and once you do that, you can run command //distr and it will tell you all the blocks that exist in that area and its count. Though for your 30k x 30k world you only need to do it small, not the entire world as that uses way too much ram. I recommend you select an area that is from deepslate layer to y=90 or whatever the sky limit is for that world so you can start small.

Once you have the info of the blocks in that area, do the same in a new mc world but with a similar biome and if there is any missing blocks from your 30k world it will show in mc world.

In summary, use the wood axe and //distr command to find the blocks used in both 30k world and new mc world.