How to create a custom activity tab in user profile?

[Arkshine]

I would recommend using Introducing Discourse developer toolbar .

Then, look for a plugin outlet where you can insert a component:

Then you can see for example:

Here is a guide about it:

Theme Developer Tutorial: 4. Using Outlets to insert and replace content

Discourse uses the Ember JS Framework for its user interface. On top of Ember, Discourse provides a number of APIs to allow themes to customize the user interface. The most commonly-used API is Plugin Outlets. These outlets are positioned throughout Discourse core, and allow themes to render Ember Components inside them. Those components are given access to some contextual information called “outlet args”. Some outlets also “wrap” part of the core user interface, which allows themes to add the…