Preheat your Traeger grill to 225°F.
Pat the turkey dry with paper towels. In a bowl, mix the softened butter, olive oil, kosher salt, black pepper, garlic powder, onion powder, smoked paprika, thyme, rosemary, and sage to create a seasoning paste.
Carefully loosen the skin of the turkey over the breast and thighs. Rub half of the seasoning paste directly onto the meat under the skin. Rub the remaining paste all over the outside of the turkey.
Stuff the cavity of the turkey with the quartered onion, lemon, smashed garlic, and fresh herbs.
Place the turkey on the grill grate and pour the chicken broth into the drip pan below the turkey.
Smoke the turkey for about 30 minutes per pound, or until the internal temperature reaches 165°F in the thickest part of the breast and thigh. Baste the turkey with the broth every hour for added moisture.
Once done, remove the turkey from the grill and let it rest for at least 30 minutes before carving.