This manga is an interesting mix of taking it seriously and not taking it seriously.
There's a certain amount of levity afforded by the fact that the MC is literally capable of bringing an end to anything, even concepts, in his weakened form.
Nothing is really a threat, so the world-building is interesting in the sense that there is more or less nothing that can even oppose the end of all existence anyways. Everything is just fun to hear about knowing that it is fully meaningless.