Trying to make the player/npcs be a billboard of a sprite but can't find a way for it to cast and receive shadows

I'm trying to make a game with a similar style to octopath traveler. The player and npcs will be 2D sprites rendered always facing the camera (Like a billboard), the rest of the game will be 3D models. The player can move on the Z and X axis, camera will follow the player but won't rotate.

The problem I am facing right now is how making the player/npc billboards cast and receive shadows. First I tried using the "Billboard Renderer" component, which seemed to be the most appropriate, but I couldn't figure out how to turn my sprite into a "BillboardAsset". Then I tried the "Sprite Renderer" component along with a simple script with transform.LookAt that makes it always face the camera, but with this method I couldn't find a way for the sprite to cast and receive shadows.

Here is how it currently looks like: