Is it possible if we were to Sadaqah our good deeds to a person who has passed away after we have done the good deed, without having that Nawaitu when we do that good deed? Like sometimes when I read the Qur'an, I do not have the intention to read it for somebody who passed away. But maybe a month later I remember, and in my Du'a I ask so that my rewards from reading the Qur'an in the past to be Sadaqah to the person who has passed away. Is that ok?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. Presenting the reward of the good deeds to others; the scholars have different opinions in this concern. However, the preponderant opinion is that it is not correct to present the reward of a deed that is initially done by a doer for himself without intending the presentation, because the acts of worship should be limited only to what is proved in Shariah. However, the Ahadith prove that it is permissible to present the reward of the deeds that are initially done for a dead person. But there is no indication in Shariah that proves that a person may transfer the reward of those deeds; he initially had done for himself, to a dead person. The evidence is the Hadith of Ayisha (Radiya Allahu Anha) that a person came to the Prophet (Sallallahu Alaihi wa Sallam) and said: my mother died suddenly and I think that if she could speak, she would have given charity. May I give charity on her behalf? He said, "Yes! Give charity on her behalf . [Reported by Imam al-Bukhari ]. It is narrated in Sahih Muslim from Abu Hurairah (Radiya Allahu Anhu) that a man said to the Prophet (Sallallahu Alaihi wa Sallam): My father died and left behind property without making any will regarding it, would he be relieved of the burden of his sins if I give Sadaqah on his behalf? He (the Prophet (Sallallahu Alaihi wa Sallam)) said: "Yes" . There are many other Ahadith proving the above fact. Moreover, there is no report from the companions of the Prophet (Sallallahu Alaihi wa Sallam) that legalizes the transfer of the reward as you mentioned in your question. If the transfer of reward had been a good act they would have done it before us. However, we are mentioning here some statements of the known scholars. Abu Abdullah al-Ubay a Maliki scholar said: If one initially recites the Qur'an to present its reward to a dead person, it will reach him like charity and Du'a. If he presents the reward of the Qur'an that he had recited, it will not reach the dead person since the reward of the reciter does not move from him to someone else . (Muktasar al-Khaleel) Ibn Muflih , in his book "al-Furooa", reported from Ibn al-Jawzi that he said: The reward of the recitation of the Qur'an reaches the dead person if one intends sending it to him/her before recitation . It is also reported in "al-Insaf": All the acts that are performed on behalf of someone need intention beforehand . Allah knows best.