What is the ruling on providing breakfast for fasting people in mosques every Thursday?

There is no harm in this announcement, because it is an invitation to do good, not a sale or purchase. What is forbidden is advertising sales, purchases, leases, or rentals, as mosques were not built for such purposes. However, inviting to good, feeding the poor, and giving charity are permissible. This is not considered an illegitimate gathering for worship, because they did not announce a collective fast, but only an announcement about breaking the fast.