How to create an activity button

I am developing a public app how can I add a custom activity button or edit one? I cannot find it anywhere, I want to add it like the public app called WhatHub does, like this:

Hey @danchy,

I believe that has been added using a chrome extension which is installed alongside the integration. From my experience HubSpot doesn’t provide any APIs that allow for that type of behaviour. It’s not officially supported within the UI at the moment.

Hi @coldrickjack do you know if there has anything changed since your reply on this topic?