I think of threats that are unknown and/or can't be adequately defended against:

* Asteroid impacts like Chicxulub.

* The Sun eventually inflating into a red giant and eating Earth, though this assumes we're both still around and haven't become spaceborne en masse.

* Pandemics such as The Black Death and, indeed, covid for a recent example.

* Social, political, or commercial intrigue.

* Cancer.

"AI" is a known threat that can be adequately defended against, so I agree with the sentiment that it's stupid to call it a "gravest of dangers".

We have a better chance of stopping a potential impactor asteroid, if it is detected early, than defending against a nuclear war.

We would have years to deflect an asteroid, but just minutes to react to a mass ICBM launch.

We have the technology available now to deflect asteroids (ironically, with nukes!), but no country has built up sufficient ballistic missile defence to shield themselves from a first strike.

The Sun expanding (or changing in any impactful way) won't be a problem for hundreds of millions of years. Nuclear war could be triggered today. The US is literally sending about a hundred billion in weapons (total) to kill the soldiers of a nuclear-armed belligerent state... right now!

Pendemics tend to fizzle because pathogens that kill too fast are self-limiting. Merely making people sick is selected for, because that leads to increased disease spread by the infectious -- but alive -- victims.

Societies, politics, and commerce have been more stable than ever in human history, and are become more stable over time, not less.

A cure for cancer in the next two decades is looking increasingly likely. Techniques such as individual rapid gene sequencing, custom mRNA anti-cancer vaccines, CRISPR/Cas9, AlphaFold 3, etc... are building up to a toolkit that will eventually allow us to treat pretty much any human illness, possibly including old age itself.