I recommend you start with the Evernote integration guide on this forum (link below)…especially to be aware of the caveats and limitations of Evernote integration at this point in time.
That said, it is possible, only on iOS with the action step, to append checkboxes to an Evernote note, but not easy at all and requires advanced scripting and understanding of Evernote’s ENML format - and then you might not really get the results you want because you cannot modify existing structures of the existing Evernote note - like to append to a bullet list that is already in the note.
If you have a requirement to append to a list of todos/tasks, you might be better off with a targeting a different platform built around tasks - like Todoist, Things, or OmniFocus.