Whilst it isn't an isekai, I can see why you said it compared said it. Afterall he effectively dies and comes back as a 'player' having an entire new world system that nobody else can comprehend and can go to places that other people don't even know exist to get items that people don't know about. So whilst it's not an isekai, I can see where you're coming from.

But yeah, Frieren was a masterpiece that I can safely say