The author of your blog post comes to this conclusion:

So do yourself a favour. Get something like bitwarden or if you like self hosting get vaultwarden. Let it generate your passwords and manage them. If you really want passkeys, put them in a password manager you control. But don’t use a platform controlled passkey store, and be very careful with security keys.

The protocol (CXP) which the article is about, would allow you to export the passkeys from the “platform controlled passkey store” and import them into e.g. Bitwarden. So i would imagine the author being in favor of the protocol.

The lock-in effect of passkeys is something that this protocol aims to solve though. The “only managed by your device” is what keeps us locked in, if there is no solution to export and import it on another device.

The protocol aims to make it easy to import and export passkeys so you can switch to a different provider. This way you won’t be stuck if you create passkeys e.g. on an Apple device and want to switch to e.g. Bitwarden or an offline password manager like KeyPassXC

The specifications are significant for a few reasons. CXP was created for passkeys and is meant to address a longstanding criticism that passkeys could contribute to user lock-in by making it prohibitively difficult for people to move between operating system vendors and types of devices. […] CXP aims to standardize the technical process for securely transferring them between platforms so users are free […].