Is it sufficient to perform ghusl with the intention of purification from semen that was discharged due to deliberately looking at something arousing, knowing that ghusl would have been performed anyway, and that it was done only once?

One must lower their gaze from what Allah has forbidden, as Allah the Almighty says: "Tell the believing men to lower their gaze and guard their private parts. That is purer for them. Indeed, Allah is Acquainted with what they do." It is forbidden to look with lust or with the fear of arousal at anyone except one's wife and concubine. As for the ghusl (ritual bath), it is valid if you intend to perform ghusl for janabah (ritual impurity) before commencing it. Combining the intention of ghusl for janabah and for cleanliness does not invalidate it.