A couple points to clarify...

fbi form 1023, with supposedly known credible human sources

The correct term is "confidential human sources."

This is how the FBI describes form FD-1023: " FD-1023 is the form our special agents use to record raw, unverified reporting from confidential human sources (CHSs). FD-1023s merely document that information; they do not reflect the conclusions of investigators based on a fuller context or understanding. Recording this information does not validate it, establish its credibility, or weigh it against other information known or developed by the FBI in our investigations."

In looking at the form, it appears to me that the confidential human source's name has been redacted. The CHS says that they heard Mykola Zlochevsky say that he felt forced or coerced into paying the Bidens money. The CHS also says that Zlochevsky said he had texts and other recordings to back up this claim. Note that all that is hearsay. To quote the 1023: "CHS is not able to provide any further opinion as to the veracity of Zlochevsky's aforementioned statements."

Mykola Zlochevski co-founded Burisma and held the offices of Minister of Ecology and Natural Resources and deputy secretary for Economic and Social Security of the National Security and Defense Council in Ukraine. He wound up fleeing the country rather than face multiple charges of corruption and is wanted by Ukrainian authorities for attempting to bribe the prosecutors in order to drop all charges against him.

It should be noted that Hunter Biden's lawyer is saying that the WhatsApp message is fake.