Here are some proposals
1. Add animated windmills and watermills with rotating blades and wheels, add forges with burning furnaces (including those in cities).
Light is streaming from windows, and smoke from chimneys what is especially picturesque at night.
Burning fires on the travellers' overnight stays and robber camps.
2. Hide all the information about settlements, size of troops under pop-ups which appear while hovering mouse over the object.
Or the pop-ups can be optional at least. Or you can do this way: At the global view at high altitude settlements can be seen. And at the closest zoom the names vanish.
Large troops and caravans can be represented in several pieces. This is meaningful, looks good and removes the digits, while the exact value can be specified in a pop-up
3. Birds can fly up with noise. This is not only aesthetics, it can be a prompt that some troops are moving through the forest.
Birds of prey can hover over a battlefield or a plundered settlement. This is meaningful too
4. If there's a ford on a river, it can be shown as shallow water with sand seen beneath the stream.
It will give a prompt on where to cross the river.
fishing boats, merchant ships and other vessels sailing in seas and lakes and along rivers.
Fish schools moving in water.
By the way, I saw birds over the water in your video!
5. Place inns along the roads for the overnight accommodation to travelers and caravans.
By reducing the travel speed universally you will add importance to roads.
Keeping the fast travel speed along the roads unchanged will make them essential. This way troops and caravans will prefer moving along the roads which will also encourage making ambushes on roads. If there are now roads in the game, you should add them!
6. Add swamps like very slow or completely impassable terrain. Add sounds - marsh owls, frogs. Decorate the mountain rivers with noisy waterfalls.
Add variety to the nature terrain: along with sunny, joyful green forests, let there be thick, gloomy forests - embarrassing movement - with windbreaks and withered trees, with howling wolves, night thunder, rain and howling winds. Bandit lairs will look great in them.
All these features will create a certain ambience and add some pleasure to the gameplay.
The more small details, various sounds you add to the map, the more interesting will be travelling through it.