In theory, I think watch time would trump retention percentage, so one longer video would theoretically do better in the algorithm...
But with that said, YouTube also values session time, and series, and depending how you brand the videos, having two could give you a potential to reach more viewers through slightly different SEO/thumbnails...
So ultimately, I'd say do whatever makes the most sense for your viewers. If you think one long video would seem arduous or off-brand, do 2. If you think they like long-form content and you'd rather present an uninterrupted video, do one.
I like to break my videos up when I can separate them by topic, but if it's literally a continuation of the exact same narrative (and turnaround time isn't an issue), I'd prefer them to be one. Just my thoughts!