So basically he was tranmigrated into formless being or spirit in a sense with a system called World Creator system like the name suggests it helped him create world or model them to his interests. He slowly started creating worlds like the first one was a copy of his world, then a magical world, after that sci fi world, then Cultivation world and so on. He slowly reached the level of high level godly being, which made him bored and with all the missions finished the system left with only leaving the mall option behind. So being bored out of his mind, he got an idea of creating worlds like MCU, GOT, LOTR....etc