Let's start with a smartphone. A user creates an account with a passkey for a service, that passkey gets stored on their smartphone, and they can use biometrics to sign in from then on. The private key is stored on the smartphone. Great.
But then how do you sign into that same service from a different device?
If it's by using a password manager, some third party piece of software, How do you sign in on a device where you're not allowed to install third party software?
1Password can't fail that hard easily. They've done great write-ups to compare their architecture to that of LastPass.
Long story short: it's the secret key that protects you: https://blog.1password.com/what-the-secret-key-does/
I would suggest to move to KeepassXC, which already shown that even when KeepassX was too slow to implement features the community was healthy enough to fork it and make it the main fork.
The wallet itself is nice, but managing the database transfers between devices isn't really something I want to do manually, especially given that devices like Apple's iPhones don't support background syncing, crippling Syncthing clients, or alternatives
I've used it on a iPhome once with a Syncthing alternative client and some alternative Keepass app. It worked very well but it was only for a month or two and I don't change passwords often so I might not realized that syncing doesn't work well.