The first suggestion would be the new express route from Ulm to Stuttgart (Tief) via Stuttgart Airport. The second suggestion would be a diesel route. The Deutsche Bahn not only has electrified routes, but also routes that are operated by Deisel railcars. From Ulm to Kempten or from Kempten to Lindau (Hafen) with the DB BR633 "Pesa Link" and the DB BR612 "Adtranz Bombardier" I know the Ulm - Kempten route and think that it will be a little interesting. Because the one from Neu-Ulm (Finninger-Straße) to Memmingen is single-lane. The common meeting point of the trains from the respective direction is Illertissen. In addition, the Neu-Ulm station is a four-track underground station. Tracks 1 and 2 are the route to and from Ulm-Augsburg-Munich and tracks 3 and 4 are the Ulm-Memmingen-Kempten route.
Hey, das Forum ist englischsprachig, wäre also schön wenn du deine Nachrichten auf Englisch verfasst. Im Titel hat es ja bereits funktioniert...