Everyone pretends that you're force to only have 1 passkey. I use 3 "passkey managers": Passwords.app, Bitwarden, YubiKey hardware key. I usually add all 3 or just two (skipping YubiKey).

On Apple devices I get neat experience out of the box, on Linux (+Firefox) I forced to use Bitwarden because Mozilla is being Mozilla.

Never had any issues ever with passkeys.

3 technological devices which I can't validate by checking if the physical piece of paper is still legible in a safe.

Yep. I use Apple’s direct support which works out of the box. I also create a second passkey in 1Password. And for truly important accounts (1Password itself, Apple, Google), I have a third copy on a YubiKey stored in a safe deposit box.