Login-with-Passkey already works with the web vault if the web browser supports an optional passkey feature called PRF. Rumor has it that this same functionality is coming to the other vaults (desktop, browser, mobile), but it has not yet hit the roadmap.
That said, Login-with-Passkey is not this FR. The proposal here is a lightweight desktop app that performs just the authentication function. Supporting login with passkeys is the subject of another feature request.