There are several subscription-free password managers available that support passkeys, e.g. Bitwarden (self-hosted), Strongbox (lifetime version available), or

There are several subscription-free password managers available that support passkeys, e.g. Bitwarden (self-hosted), Strongbox (lifetime version available), or KeepassXC. It's unfortunately not quite the same level of portability as passwords, as I don't think there's any standardized export/import format yet, but these options are significantly better than Apples's and Google's closed ecosystems.