Okay, having it so that the MC was a (presumably senile) old man before getting Isekai'd is a pretty clever way to justify/ground a "MC is Super OP but he and everyone else thinks he's trash" story..... but the execution in this particular story wastes it. After the second chapter I can't suspend my disbelieve that the MC (and those around him) would not realize his power, and the premise goes from being humorous to being frustrating.
I might give the manga another shot when there's more chapters available, since I do enjoy Isekai trash, but the first 3 chapters don't really jive with me.