I do not understand the basis for your factual premise that the witness has already directly contradicted their claim of a crime. You may have good reason for this, but I just don't know this case well enough.
I am in disagreement that the napkin could only be used to "refresh" or "rebut" (at least in Canada).
I am not sure I understand what your basis is for claiming that the napkin is written "opinion".
I am going to give you a very simple example to explain my position: Medical negligence. It is very common in medical negligence cases that a doctor who is sued for misconduct says they have absolutely no memory of what happened between them and the patient. In that case, the doctor relies on their contemporaneous notes of the meeting as their evidence of what was said.
The notes do not in any way "refresh" the doctor's memory. But the note is still admissible for the truth of its contents on the basis that the doctor authored them, and that they believe the notes were made contemporaneously. That is sufficient for admissibility.
Well then you aren't even discussing hearsay within the meaning of US law. You're talking about an instance when the author of the writing is already testifying, and the note gets in that way. The same rules would apply in the US, and we wouldn't refer to the note as hearsay in that case.
In this instance, and it sounds like you aren't too familiar with the case, it's unlikely that said cocktail napkin would get admitted in such a fashion. The short of it is: The defendant is charged with lying to a federal officer. The only evidence of said lie are the handwritten notes of the former FBI director that reads "Says he's not working for anyone." Said director has already clarified, to both investigators and the public, that this note was more of quick take an not a dispositive declaration that the defendant ever made such a statement. Essentially, "I honestly don't remember and he could have very well told me that he was working for X, Y, Z."
My point was only that this is a really weak case. So from the prosecutions standpoint, what can they do? They can't admit said cocktail napkin into evidence by itself without calling said FBI director to testify, as that most certainly would be hearsay under US law. They could call said director to testify, and then when he gives his testimony on said meeting, try to then bring up said cocktail napkin to confirm, rebut, whatever. But this seems pretty fucking stupid, given that the guys on record pretty clearly contradicting the prosecutions claim that he was lied to.
So my point was that: cocktail napkin by itself = hearsay. Cocktail napkin in support/rebuttal/some other exception to testimony = ok, but tactically stupid.
All in all, this is a pretty partisan case. This is all being brought by a special investigator, Durham, appointed by former AG Barr as part of the "investigate the investigators," after many US agencies concluded that Russia had interfered in our election to push Trump. And after five years, this is the single charge they've arrived at. And you can see how it's playing out in the right-wing media world here, with them declaring that this is proof that Trump was "framed by Clinton," or some other vague nonsense that doesn't even fit the facts. Even further, it's a stretch to call this a "lie" within the meaning of the english language or realm of common sense. In order to get there, in addition to having to believe that the cocktail napkin was the accurate statement (and not the FBI directors clarification on what he meant when he wrote it), you'd still have to conclude that Sussman (the defendant), was lying because although he was not counsel for Clinton when he said he wasn't working for anyone; because his previous work for a different client (the federal government) was later cited by other members of his firm that were representing Clinton, therefore, Sussman himself was working for her. And that's a pretty big stretch.
It would be the equivalent of me asking you if you represented Smith; you truthfully say "no,"; then I point out that two other attorneys at your 3,000+ member firm are representing Smith. And because they cited some work you produced when you represented Jones, well then you are a liar because you represented Smith. And I don't see how anyone could conclude you represented an individual just because you were cited by someone who actually did. If that's the case, then I've "worked for," a whole host of people I've never met, talked to, filed anything on their behalf, or taken money from.