For the accounts that are highly important, you might want to use only keys that are bound to a device like a computer, phone, or hardware security key. This would require a bit of manual management as you swap out devices and hardware keys but for a limited number of important accounts this should be feasible. For all the other general accounts, storing them in a password manager can continue to be the most convenient way to use them. The Google/Apple/Microsoft solutions take this second approach and allow them to be synced across devices.

As for the portability, it's still relatively early and I don't think there's a standardized format to export passkeys into. It's only a matter of time before things settle down and different password/passkey managers support importing and exporting to at least one format that will work.