Just wait until you lose your devices

all at once? I find that unlikely

No one has ever had a whole house disaster after all!

Sure, but iCloud still has my entire phone encrypted and will backup restore to a new device, I would imagine my Passkey which is stored in the Passwords app regardless would be fine. Alternatively you can put Passkey in your Bitwarden vault as well.

You don't travel? Easy to have all your devices stolen at once on the street.

Backup codes somewhere safe. I mean if you're traveling and your bank cards or passport gets stolen you're similarly in trouble, but there's a contingency plan for those kinds of things.

I thought the working group making the standard was threatening to blacklist any implementation that allows passkeys to be exported for backup, no?

Yes, but unlike with 2FA and SaaS, there's always some recourse. Worst case, you may need to physically visit some bank or government branch, send some registered letters and/or notarize some statements, but there's always a way to recover from losing your ID, passport, or access to a bank account.

Until similar process exist in digital space (read: is legally and culturally forced on SaaS vendors), 2FA is frankly dangerous - it demands standards of diligence and long-term care that not even government affairs do. The back-up codes users are instructed to print out and store securely? No other document in most people's lives requires such long-term protection.

I can't say that I fly with everything valuable I have to my name, no. I leave my iPad and my Laptop at home usually, unless I am staying within my state visiting family and even then, I'm pretty sure my iCloud backup will still work on a brand new iPhone, heck I know it will, since it pushed everything to my newer iPhone even things I don't sync were in the encrypted backup of the whole device.