Plot.bin file format

I want to understand my farmer’s plot.bin file format.

Is there a document describing about this?

I have tried to understand this by code, but the thread pool make it difficult.

Thread poll has absolutely nothing to do with the format. All the logic for working with it is in subspace-farmer-components crate and you can also watch https://www.youtube.com/watch?v=aHZ5LbFpfpw and/or specification for details (though it doesn’t include things like checksums, which is an implementation detail).