Surprisingly not. It's far future Earth. MC's power just allows him to create anything that has ever existed on the planet which is why he knows of things. Honestly not a big spoiler because it's not relevant to the plot at all and the reveal of it is pretty much brushed aside in a few sentences in the novel.
@Urtag & @Chaos_Knight are we really being that strict with the definition? Modern human memories in a strange/magical setting would IMHO put it into isekai territory. I'd mark Alice in Borderland as isekai as well..