The main character saves another world and returns home to find that everyone thought he was missing or dead. He ends up living with and protecting his childhood best friend and her daughter.
I think it only has a few chapters.
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This is Isekai Kaeri no Daikenja-sama wa Soredemo Kossori Kurashiteiru Tsumori desu (The Great Sage Who Returned From Another World Wants To Live Quietly).
Saito was reincarnated to the other world at the age of 15, becomes the Great Sage, and defeated the Demon Lord. Shortly after that, the door connecting the other world and the real world opens, and Saitou return to Japan with the power of the Great Sage. However, 19 years have passed in the real world. Saito, who was drifted away for so long, met his childhood friend Kanako, who’s now a single mother. But it seems like there’s someone who’s targeting Kanako’s life…
The synopsis is a solid match for the question. He saves another world and returns, with 19 years having passed in Japan. There's no explicit mention of thinking he was dead, but it's clearly implied.
This manga is from 2021, and according to manga updates, only 3 chapters have been scanlated, which also matches the question.