Avast secure browser

how do I disable this stupid secure browser from getting added to the taskbar and putting it as my default browser

First, I’m an Avast user and not an Avast Team member and I don’t use the Avast Secure Browser.
I modified your question and did a Google search on it.

You could have tried this as a modified search.
Stop the Avast secure browser being added to the taskbar and set as my default browser

You might also want to check this old Avast Topic - though things could have changed since then.