Tilemaps generally lack "global" shading (e.g. a house in one area casts a shadow on a neighboring area), and without a significant increase in workload through specifying actual 3D representations of tiles, it cannot be calculated automatically either. Instead, it could be a reasonable option to let users "paint" shadows onto the tilemap.
Analysis
Rpg Maker has a similar, but very low quality variant of this, where users can draw (fully opaque) shadow sub-tiles at 1/4 the size (1/2 the edge length) of the main tile.
This is a potential feature exploration issue without a clear roadmap or technical path so far.
A first prototype of this could be achieved by simply adding a new tilemap layer via the editor and assign a special "shadow" tileset to it, which contains various shadow tiles with sharp and soft edges.
Overall, paintable shadows should be regarded as more of an "Ambient Occlusion" layer than one for actual geometric shadows, since it's more general purpose.
Probably should explore this issue with someone experienced in using tilemaps in the traditional "map making" sense.
Summary
Tilemaps generally lack "global" shading (e.g. a house in one area casts a shadow on a neighboring area), and without a significant increase in workload through specifying actual 3D representations of tiles, it cannot be calculated automatically either. Instead, it could be a reasonable option to let users "paint" shadows onto the tilemap.
Analysis