Earlier quoted context omitted.
(IAAL but this is not legal advice.) It’s not libel. Defamation requires a false statement of fact . Marking a website as “unsafe” is an opinion .
In my opinion, a .online domain is unsafe. 99% of people only visit ".com"s unless they clicked a scam link. Completely blocking the site is overkill, but the browser should warn you about it like it does with non-SSL sites.
In other countries local TLDs are of course normal (e.g. .it for Italy, .za for South Africa, .cn for China...) and not only used for scam links.