Kami-sama nanka Shinjitenai kedo, "Kami no Kiseki" wa Bunmawasu: JIbun Katte ni Mahou wo Fuyashite, Isekai de Musousuru

When 47-year-old single programmer Ritsu Hisahashi opens his eyes, he finds himself reincarnated as a boy named Mika in a poor village in another world. In a world where magic called 【God's Miracles】 exists, he leverages his knowledge from his previous life, his drive to take action, and his thirst for discovery—secretly training his magic alone, unnoticed by the adults... Eventually, a classic tale of growth about a boy who brings light to the kingdom!! Source: MU