Is eating Mawlid sweets unlawful before, after, and on the day of the celebration, and what is the ruling on buying them, especially since they only appeared during these days?

Celebrating the Mawlid is an innovation introduced by the Ubaydis. Purchasing Mawlid sweets at the time of its celebration is a form of assistance and promotion of it, and indeed, a way of establishing this innovated Eid. The clear proofs from the Qur’an and Sunnah (definition) unanimously agree that the Eids in Islam are only Eid al-Fitr and Eid al-Adha. Anything other than these is an innovated Eid, and it is not permissible to practice it or assist in it in any way, whether by eating, selling, buying, or anything else, because that falls under cooperation in sin and transgression.