The Hunter B laptop in FBI possession is confirmed to be legitimate and tied to Hunter Biden via his iCloud account on the laptop. No one questions who was the owner of the laptop when the repair shop took possession and subsequently gave it to the FBI, or authenticity of its contents.
"When the FBI took possession of the device in December 2019, they notified the IRS that it likely contained evidence of tax crimes."
https://www.19fortyfive.com/2023/06/the-biden-family-is-in-some-serious-trouble/
However, the IRS investigators testified they were prevented from examining the computer evidence as prosecutors refused to share the laptop.
https://waysandmeans.house.gov/smith-testimony-of-irs-employees-reveals-biden-irs-doj-interfered-in-tax-investigation-of-hunter-biden-revealing-preferential-treatment-for-wealthy-and-politically-connected/