Tear the oyster mushrooms into medium, wing-sized pieces, keeping some of the stem base intact to hold clusters together.
In a bowl, combine the plant-based milk and lemon juice or vinegar. Let it sit for 5 minutes to curdle slightly and form a vegan buttermilk.
In a separate bowl, whisk together the plain flour, cornflour, garlic powder, smoked paprika, salt and black pepper.
Dip each mushroom piece into the buttermilk, then dredge in the flour mixture to coat thoroughly. Press gently to help the coating stick, then set aside.
Preheat the air fryer to 200°C (392°F). Arrange the mushrooms in a single layer, spray or brush lightly with olive oil, and air-fry for 10–12 minutes, flipping halfway and brushing or spraying again, until crisp and lightly golden.
To make the buffalo glaze, mix together the hot sauce, olive oil, and maple syrup (if using) in a small bowl until smooth.
Toss the crispy mushrooms in the buffalo sauce until evenly coated, then return them to the air fryer and cook for a further 6 minutes at 200°C (392°F), until glazed and crisp at the edges.
To prepare the vegan ranch, whisk together the yoghurt, vegan mayo, lemon juice, garlic powder, dill, chives or parsley, salt and pepper. Add a little water if needed to reach a creamy, pourable consistency.
Serve the buffalo mushrooms hot with the ranch sauce on the side for dipping. Garnish with fresh herbs if desired.