OK, Arahants still generate manosankhara. But there is no akusala gati. Thus those manosankhara are not defiled with gati. As you say in the post Difference Between Tanhā and Upādāna, #4:
“Then manō saṅkhāra arise automatically according to gati. That will happen as long as we have taṇhā (either via kāma rāga or paṭigha; avijjā is present in both cases). We automatically get attracted.”
So tanha can arise if asobhana or sobhana cetasika are included in the cittas and paññā is absent.