The FBI verified the authenticity of the diary, not its contents.
As to the credibility of ProjectVeritas, here is what their own CEO had to say:
Two weeks ago, Hannah Giles, chief executive of Project Veritas, quit her job, saying in a social media post she had “stepped into an unsalvageable mess — one wrought with strong evidence of past illegality and post financial improprieties.” She said she’d reported what she found to “appropriate law enforcement agencies.”
None of what you posted is true, as much as your little MAGA heart wants it to be.