For those wondering like me: Blake3 generates hashes of at least 224 bits, not, as a literal reading of that comment indicates, 40 bits (which would be bad for file deduplication, giving you a 50% hash collision after around a million files)

Yup sorry if I mislead people. I usually use 10 hexdigits (40 bits) but no matter how many there are, it's the x bits of the beginning of the checksum that are verified against the hash (in the examples I gave 40 bits).

I wasn't very clear.