There are two ways to work with Vue3 - Options API (The way system is organised is inherited from Vue2, with data() ) and Composition API (the new way). Docs exist in 2 versions, you can switch between versions of docs for the API you prefer. I've came from Vue2 background, I've switched to Composition API

Now people can go about putting variables all around the place?

If they so desire, yes. It's up to programmer to organise his workspace.

It's good for small applications but when applications are enterprise levels with people coming and going, how is Vue handling this?

Exactly the same way as any other large framework handles it - you get a set of internal guidelines and best practices to follow and organise and document your work accordingly. You also train new people to follow guidelines.

The ability to relate to OOPs seems to be missing

I don't understand that you mean by that. OOP is how you organise your code based on JS capabilities and/or build your components. I don't see how it is changed depending on API.