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It's probably not something the app or web page should have any visibility or control over. It's more something the browsers and OS should allow a straightforward selection of where you want your passkeys stored (ideally something you can configure the default for globally). But of course the OS and browser vendors are trying to compete to do it, so they're not incentivised to make it obvious or fair.
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>I haven't yet found a way for a mobile app or web page to explicitly signal to the device that the passkey to be created should live in $password_manager and not whatever built-in/on-device key-store exists.

On Android 17 (on Pixel) you can select the password service under Settings -> Passwords and passkeys -> Preferred service.

If you have an alternative password manager installed, it will be listed there along with Google's own password manager. iOS has a similar setting but I don't know exactly where off the top of my head.

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> On Android 17 (on Pixel) you can select the password service under Settings -> Passwords and passkeys -> Preferred service.

I have this set to my password manager but I still can't _use_ the pass-keys in my password manager to sign in to most apps.

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"Most" apps? So it works in some apps, but not others?

Setting your preferred password/passkey manager on Android 17 to 1Password works fine in Chrome and Firefox to log in to any site, presenting passkeys managed in 1Password. It also works in all of Meta's native apps. (I'm pretty sure it works the same in Bitwarden.)

Whatever issue you're having, it's not an inherent limitation of Android passkeys. It might be a bug in your passkey manager…?

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Works fine on iOS. All my passkeys are in 1Password, and every prompt to use or save a passkey goes through 1P. You can also control which password managers are active on iOS (eg, I disable iCloud passwords, and only allow “autofill from” 1Password.)

So yeah, this is cross platform on iOS, macOS, Windows, and Linux.

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