The keys aren’t stored in the browser. The browser just forwards to the hardware.
Switching from one password/-key manager to another is going to be more of an issue.
But you should be able to add an additional passkey once logged in to an account, just like how you can have multiple hardware 2fa keys now.
Then you could manually migrate accounts that way, which is painful, of course, but you wouldn’t be completely locked in.
I use both chrome and safari, and hate they don't use the same password store anymore (chrome used to just use keychain).
But on iOS, you can at least fill in passwords using chrome as well
Switching from one password/-key manager to another is going to be more of an issue.
But you should be able to add an additional passkey once logged in to an account, just like how you can have multiple hardware 2fa keys now. Then you could manually migrate accounts that way, which is painful, of course, but you wouldn’t be completely locked in.