How to integreate TypeScript into existing project?

My goal is to not to touch current js and vue components. but I want to be able to start to use typescript with new vue components or js. but I could not get it works.

What I have tried: First thing is to run vue add typescript. And after it installed some things it asks me questions:
? Use class-style component syntax? No
? Use Babel alongside TypeScript for auto-detected polyfills? Yes

then it convertes all my js into ts. I need to manually fix all of them…that is a bit chunk of work to get it done.

So I am wondering is there a way to do that without forcing the whole project to change to typescript?

I am using vue cli 3.