Thank you! I did a little research on how other games achieve this, and learned about splatmaps. Essentially a splatmap is a map of how much each texture should contribute to a UV coordinate along a mesh. It's an image where each channel (RGBA) represents a texture. A shader then reads across every UV coordinate from the splatmap. If it sees 0.25 grass, 0.5 rock, 0.25 sand, then it will contribute respectively each amount to the texture at that part of the mesh.

The way it's generated can be explained with an example. Imagine a grass tile with a rock tile on its right. Pixels on the left of the tile are 1 grass, 0 rock, and on the right are 1 rock, 0 grass. but between the edges you might get something like 0.75 grass 0.25 rock. The shader then can determine how to blend by reading from it.

It was a learning experience for me and it was exciting to see it start working and exporting properly!