I think the UK is that way.

You could call out Lord St. Buggering-Little-Boys, complete with films, DNA evidence, and witness testimony, and still lose (and be on the hook for legal fees).

Japan is like that - making someone look bad by publicizing their provably-true behavior is considered defamation

But he already accused Neimann of cheating ... the slander is already there.

If I were Neimann I would actually sue now.

That's why Carlsen is being very careful at what he does.

He hasn't said anything beyond provable facts, and let people read into his actions what they want.

Suing someone for defamation because they resigned to you in a tournament is going to be a pretty high bar.

Neimann has already admitted to cheating in the past, so that claim is dead.

You're allowed to make "very strong implications". The other word for that is "opinion". You're in trouble if you say "I've been given secret information that shows Neimann cheated at the Cup", but if all you're saying is "based on these factors, which by implication you yourself could evaluate, I believe he's cheating", you're offering an opinion based on disclosed facts, and that defamation claim won't survive dismissal.

(I'm not a lawyer, I just nerd out on this stuff, happy to be corrected).