each opportunity record has a button that is used to run different processes. This "Run Process" button, has a list of items, "Processes", and I would like to know how can I execute my method after the button is fully rendered, including its items.
Unfortunately, there is no method that is triggered after all elements on a page is rendered. However, we recommend you to try to use onEntityInitialized method. It guarantees that HTML and all data for entity is already loaded. Also please take a look at the setTimeout function in js.