Is it permissible to memorize the Qur’an with the intention of it being an ongoing charity (Sadaqah Jariyah) on behalf of a deceased mother?

The reward for charity and supplication for the deceased reaches them. Enduring charity is an endowment (Waqf), which means holding the principal and dedicating its usufruct. Memorizing the Quran is not an enduring charity, but it is a righteous deed, and it is permissible to dedicate its reward to the deceased.