Is money earned from selling goods in which I violated the landlord's condition considered unlawful (haram), knowing that selling these goods is permissible in itself, and that informing the landlord of my violation will lead to the termination of the contract?

The fundamental principle is that a tenant may sell whatever permissible goods they wish in the rented premises, unless it is more harmful than the activity agreed upon. If the landlord stipulates to the tenant that they are not to sell certain goods, and they contract upon that, then the condition is valid and must be fulfilled if the landlord has a legitimate purpose; based on the Almighty's saying: (O you who have believed, fulfill [your] contracts) and the Prophet’s (peace be upon him) saying: (Muslims are bound by their stipulations). If the landlord does not have a legitimate purpose for the condition, then it is not obligatory to fulfill it. Violating a valid condition is a sin, but the sale itself is valid, and its proceeds are lawful. The tenant must repent and fulfill the condition.