This is a big problem I have with "just works". Everyone is used to services only allowing a single password. I know the answer to this, but it's not clear in the marketing or how it's explained to normie end-users: Won't creating a passkey erase my password? How do you sign in on another device? Won't that change the passkey and lock me out from the first device?

Creating a passkey generally won't erase your password, no. Using a passkey generally requres a password manager or yubikey, so you can set that up on the other device and use the same passkey.

it just a lot of complexity and i don't want to deal with it but i have to because of all these dark patterns. sometimes i enable pass key and don't even notice.