[2022] Is there a limit on blocks?

There is technically a limit. Much like minecraft, the game is made up of 16x16 chunks that extend from bedrock to a certain point in the sky. In 7dtd's case it's bedrock, then 252 height of buildable space- Of which roughly 194 of that exists above ground level. So in total, there's 64,512~ blocks per chunk times the number of chunks.

Thing is, Every space, even the 'empty' ones are technically filled. Just the empty ones are filled with 'air' blocks.

But, the actual answer to what you're trying to discern is that no, there is no maximum limit tot he number of blocks any given user can place or remove from the game world. You wanna build a 5,000,000 block castle, by all means.