A route can only have one POST handler for example. It logically makes no sense that it has two POST handlers. That's not how REST works.

Think from the other sides where people want to treat it as a single end point which contains many functions, ntohing to do with how POST works or how REST works

for example, how do we have them in one single file under /api/user/route.ts

export async function registerUser() {}

export async function loginUser() {}

export async function activateUser() {}

You don't because that's not RESTful

Next's route handlers are exposed as a REST API

You have to map those functions onto proper methods

Or other routes

You have to map those functions onto proper methods
Or other routes

^ Like how, any example that I could refer?

creating other routes makes absolutely no sense as in we have to create these just to get 3 api routes working /api/user/create-user/route.ts , /api/user/login-user/route.ts, /api/user/activate-user/route.ts

Because you are not familiar with RESTful API design. Thinking of users as a resource, registering them means creating a new user, as such a POST /api/users is probably the most idiomatic for that. Activating a user means updating an existing record/resource and thus it's likely to end up being a dedicated PATCH /api/users or PUT /api/users request. Personally, the former makes more sense by updating a single flag and setting the record to be active. A login is most likely a POST /api/auth or POST /api/login attempting to create a new session or similar.

thanks!

appreciate your long post

in short we utilize search query / slug to do more customized functions such as get disabled users, get active users etc in GET method?