"Our lawfully issued subpoena to Hunter Biden requires him to appear for a deposition on December 13. We expect full cooperation with our subpoena for a deposition but also agree that Hunter Biden should have [the] opportunity to testify in a public setting at a future date."
No one said he cannot testify publicly. He's just going to be deposed first. This is standard protocol for not just congressional hearings, but pretty much any kind of civil litigation.