Hey @Anigma,
the only older Nitrokey that can store Passkeys is the Nitrokey FIDO2, which supports 10 Passkeys.
The Nitrokey 3 currently is also restricted to 10 Passkeys, but we are currently working on increasing this number.
The background for this is that Passkeys are in fact nothing new, they exists for quite a while within the FIDO2 standard - but mostly known as “discoverable credentials” and/or “Resident Keys”. Now that the “big players” move this topic forward (mostly from a marketing perspective, e.g., Android-support for FIDO2 tokens is still missing) and have given it a fancy new name, more services will support Passkeys and we will therefore also increase the number of available Passkeys that can be stored on the Nitrokey 3.