Hey, remember when all the intelligence poobahs swore up and down that the laptop was Russian disinformation? No? Well, we do...
https://www.politico.com/news/2020/10/19/hunter-biden-story-russian-disinfo-430276
The letter did what it was intended to do: Make people think it was the Russians, while leaving the door open for the signatories to say: "Well we never said it was the Russians, we said it may have been."
The operative term for it is: "probable deniability".