The document there is laughable too, because KeepassXC is listed as "not performing User Verification" when it demands manual authorization per request. But this isn't good enough for the passkey people. Ultimately, I see any FOSS option being effectively banned from most services and all important ones. It's a parallel to how you must now be on Cloudflare's nice list or be banned from the majority of the internet.
I proudly print my entire KDBX file including passkey private keys and I encourage my elderly parents to do so too.
Lightning strikes (and assisting people with cleanup and repair from them) have taught me that there are definitely a class of threats that will leave me with paper but possibly no technology until I can go buy a cheap laptop to restart my digital life, SO BEING ABLE TO BACK EVERYTHING UP IS ABSOLUTELY ESSENTIAL.
His website says he's in Boston, so I seriously doubt he's ever seen what lightning can do or dealt with a hurricane or tornado.
In general, if you're in the FIDO Alliance and had anything to do with the kind of micromanagement that passkeys can allow, FUCK YOU. Go get a job at Walmart as a greeter. We'll all be better off.