You can indeed plead the 5th to a grand jury, if your testimony might conceivably be used to prosecute you. Similarly for a government form: the government can

You can indeed plead the 5th to a grand jury, if your testimony might conceivably be used to prosecute you. Similarly for a government form: the government can't slide you a piece of paper and compel you to bear witness against yourself outside of a courtroom. But that isn't remotely close to what's happening here, because none of the information the IRS asks taxpayers for can be used to prosecute them (because it isn't illegal to own digital assets). Edit: s/ask/compel/