
using this line:
gameObject.AddComponent<attachScript>();
Unity lets me set this all up but then I can not get the assignment code line correct.

using this line:
gameObject.AddComponent<attachScript>();
Unity lets me set this all up but then I can not get the assignment code line correct.
Yes, you can’t use a variable in place of a Generic Type parameter.
Look at the overloads for AddComponent: Unity - Scripting API: GameObject.AddComponent
One overload allows a Type variable instead. You should be able to grab the type through some means and use that in the overload. I can’t remember the proper syntax off the top of my head; nor am I at home to test for it admittedly.
I found references on Reddit and came up with this very simple guarantee:
public MonoScript attachScript;
System.Type m_ScriptClass = attachScript.GetClass();
gameobject.AddComponent(m_ScriptClass);
After this code then methods access can be gained.