The reason your character won’t walk off is because the Top Down game’s movement is based off a nav mesh. If you click in the viewport and hit the ‘P’ key, it’ll show the nav mesh itself. All of the movement that the character makes is limited to the green areas of the nav mesh, which are normally flat surfaces that are within the NavMeshBoundsVolume which can be found in the world outliner.
The answer to making the character jump down comes in the form of a nav link. This can be added like most other objects and will give you a left and right node for the link. Nav links, by default, only work in the downward direction and require special functions to allow a character to go upward. Simply place the left or right node at the top of the ramp, then the other on the ground in the direction you’d like the character to jump off. The limitation of this is that they will only jump off from that spot. Also be sure that the settings of the nav link match the direction you’re making them go. In example, if the left node is at the top of the ramp and the right is at the bottom, set it to left to right. If you set it to both ways, the character will attempt to go up that way as well even though he cannot.
When it comes to the character not wanting to walk on top of the cube, that is due to the nav mesh’s bounds. If you scale the nav mesh to encompass the cubes as well as the floor, it should generate a nav mesh for the top of the cubes as well, allowing the character to walk on them.
Hope this helps!