All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
There is no harm in this if it is intended to conceal the beauty of the baby and shield him from the evil eye.
Ibn Al-Qayyim wrote, "Chapter: Among the treatment for the evil eye and seeking protection from it is to conceal the beautiful features of the person who is feared to be affected by the evil eye with something that would ward it off; Al-Baghawi said in his book Sharh As-Sunnah that ʻUthmaan, may Allah be pleased with him, saw a handsome boy and said, 'Blacken the dimple in his chin lest the evil eye affects him.'" [ Zaad Al-Ma’aad]
However, if people believe that drawing the black dot has a real effect in itself, then this is a false belief, and it is impermissible for the Muslim to act upon it. Scholars stated that it is impermissible for the Muslim to believe that something brings about benefit or wards off harm unless proven by the Shariah or by tangible proof.
Shaykh Saalih Aal Ash-Shaykh said, "People have countless false beliefs regarding warding off the evil eye. In brief, anything that they use while believing that it is a reason in itself while Allah did not legislate nor decree it to be a means of achieving such an objective, it is impermissible to use it."
Shaykh ʻAli Mahfooth said, "Among the religious innovations are the rituals practiced on the seventh day after the child's birth, like decorating a jug-like vessel with different kinds of adornments and flowers, sprinkling salt, lighting candles, beating with a brass mortar and pestle (to make loud sounds next to the baby), chanting some known lyrics, and hanging some grains and salt on the baby.." [Madhaar Al-Ibtidaaʻ]
Please refer to fatwas 51353 and 89017.
Allah knows best.