How to simplify login and registration when you can’t use social login?

What is a good alternative to the traditional registration and logging in methods, other than social log in? I have a project that I'm building that I cannot employ the use of social logins-in.

I would need for it to be quick, as users usually prefer not to create new accounts through username/password every time they find a new site. It would also need to be secure, as I am asking for some sensitive information, and a lot of details.

I know this may seem like I'm overthinking it, and thinking of a solution for a problem I'm creating (letting go of traditional and social login), but I remember when social-logins became a thing, and it became one of the best UX practices, making users comfortable logging in or signing up. It was, and still is, an amazing solution.

I'm wondering if there were to be another evolution, what would it be? It would have to work on both Mobile and Web. What are the limitations? What are the possibilities?