More Scripts can be downloaded here: https://liquidandscripts.com/collections/free-shopify-scripts

Shopify Scripts - Buy X Quantity, get Y% off

DISCOUNTS_BY_QUANTITY = {
  10_000 => 20,
  1_000 => 15,
  100 => 10,
  10 => 5,
}

Input.cart.line_items.each do |line_item|
  next if line_item.variant.product.gift_card?

  quantity, discount = DISCOUNTS_BY_QUANTITY.find do |quantity, _|
    line_item.quantity >= quantity
  end
  next unless discount

  message = "#{discount}% off when buying at least #{quantity}."
  line_item.change_line_price(
    line_item.line_price * (Decimal.new(1) - discount.to_d / 100),
    message: message,
  )
end

Output.cart = Input.cart

how would I do this by a specific tag "discountable"

What if I have 2 variants of same product?
I want to give discount if I have 1 variant x 2 quantity, or 2 variant x 1 quantity.
Ex. This only works if you get 2 blue variants of same t-shirt, not when you buy 1 red and 1 blue variants of same t-shirt.