What is the ruling on reciting the aforementioned incantation, and is it considered major shirk, or disbelief (kufr), or merely forbidden (haram)?

Incantations (ruqya) that contain talismans or incomprehensible words are forbidden, and most likely they are polytheistic incantations (ruqya shirkia). They may lead their practitioner to major or minor shirk (polytheism) depending on their belief. If the servant relies on them, trusts in them, and attributes benefit and harm to them, then that is major shirk.