KeepassXC is a good client that lets you handle your data how you want. I wrote a pro-Passkey blog post here[1] that explains how to do your own syncing, though I later discovered Passkeys are explicitly built to support proprietary software vendor lock in and had to revoke my support. If you are concerned about being able to control your own data outside of the big tech ecosystem, I strongly recommend avoiding passkeys entirely. It is possible for now, but they are not built for that and the spec authors are actively hostile to you managing your own data.

[1] https://www.smokingonabike.com/2025/01/04/passkey-marketing-...