The Babylon Bee just posted at least ten articles saying Biden did various things that Hitler did ("names self Supreme Führer", "announces invasion of Poland", "swallows cyanide capsule in underground bunker", etc). Is that defamation?
In practice, almost certainly not.
A defamatory statement, in the context of a public figure, is a statement of fact about a person that tends to hurt their reputation, stated with an intent that the factual statement is to be understood by the audience as true, that the person making the statement knows to be false or makes with reckless disregard for the truth or falsity of the statement. (This is the New York Times v. Sullivan actual malice standard.)
The case law of defamation, moreover, applies a sophisticated reading of the alleged defamatory statement that takes into account the subtleties of advanced ways of using language and not mere a crabbed or unduly literal reading of the allegedly defamatory statement.
Pretty much every statement of fact made by the Babylon Bee, a satirical publication akin to the more familiar publication The Onion is not intended to be read as a non-fictional, fact checked account of actual facts. It is inherently a periodical that publishes fictional parodies.
The context of the whole page which a comment indicates drives the question, also really has to be taken into account as a whole, in particular, is so patently absurd and obviously false, that the claim there the publication is sincerely making a statement about facts in real life is easily overcome. An image of the page is as follows:
Taken as a whole, the actual intent of the series of posts is to make fun of Biden's political opponents who baselessly compare Biden to Hitler when the comparison is not warranted, and not to harm Biden's reputation at all, in a subtle diss of his histrionic conservative critics, not Biden himself.
Also, comparisons to Hitler have a strong component of opinion to them in most cases, and the bar for finding that a public figure like the U.S. President, in the context of a politically commentary in satire form has been defamed is extremely high.
While it might be possible to imagine some very specific fact pattern that could overcome this legal standard (especially if it hit upon the personal non-official conduct of the President in some way completely unrelated to his official duties, which it is hard to imagine a Hitler comparison being), in practice, it just wouldn't happen.
Satire and the related Parody are expressly considered protected speech in the free speech clause of the 1st amendment.
Satire is considered a very important form of criticism. Although plenty of satire is politically motivated and often offensive. These offensive utterances may still hold opinions worth protecting.
A lot of parodies and satire give meaningful and constructive criticisms in regard to many social ills. It also is an outlet for individuals to criticize their government. This freedom is a hallmark of a healthy democracy. Satire to a great deal protects the ability to express culture, science, and artistic expression
Remember Free Speech does not only apply to people you agree with.
In The Friends of Voltaire, Evelyn Beatrice Hall wrote the phrase: "I disapprove of what you say, but I will defend to the death your right to say it" This quotation – which is sometimes misattributed to Voltaire himself – is often cited to describe the principle of freedom of speech
The Supreme Court ruled on an almost identical case in Hustler Magazine v. Falwell, 485 U.S. 46 (1988). Jerry Falwell was a famous televangelist, and Hustler printed a parody liquor ad (text NSFW) which had Falwell recounting having drunken sex with his own mother (in an outhouse, no less). Falwell sued for libel and intentional infliction of emotional distress, but the Supreme Court held 8-0 that Hustler was not liable because the ad parody was "not reasonably believable".
The situation here is exactly parallel: a public figure was alleged, in an absurd parody, to have done something scandalous. In each case the publisher probably did act with "actual malice"; they obviously knew that the claims were false, and deliberately set out to subject the target to ridicule. But since no reasonable person could believe that the claims were actually true, there was no libel. In some ways the Babylon Bee claims (e.g. "Biden announces invasion of Poland") are even less believable than those in Hustler, or at least, a lot easier to disprove.