Interesting suggestion! I was there last week, on a golf course near the Aschau branch (which is also called Chiemgaubahn). It’s way to short though, would likely need to include the Rosenheim to Traunstein line at the very least. Beautiful area with lots of rolling stock variety!
You can also develop the Prien am Chiemsee to Aschau Route as a DLC for Train Sim World 3 that's my Suggestion too
This is a section of Rosenheim Traunstein Salzburg line Freight services Rosenheim Gbf to Salzburg Gnigl where they are separated using a ÖBB 1163. Best value go all the way to Salzburg instead of ending in Traunstein from Rosenheim.
I will also like the route Rosenheim to Salzburg and the route Prien am Chiemsee to Aschau both we can also do both routes as DLC in Train Sim World 3