Couple more suggestions, they’re strictly battle simulators but very good ones. Think Total War’s battle scenarios with more depth to them.
Ultimate General is easy to pick up but still fairly challenging.
Scourge of War is very hard and has a bad UI, but it’s main draw is having scenarios covering everything from small skirmishes to multi day battles, and being able to take command at any level in the hierarchy.
It plays as a straight RTS if you want, but you can choose to have the camera locked to your chosen commander, and receive/send orders by courier, which makes it unlike anything else I’ve played.