I'm learning to sculpt my characters now and when I export the FBX file from Blender to Unity the Mesh has a giant hole in the face. How can I prevent/Fix this? It works just fine in mixamo.
Some of your faces have inverted normals. Unity interprets them as backfaces and the default material shaders cull them (don't render them).
The solution is very simple. Select all your models verticies in blender edit mode press alt+n and select recalculate outside. After that you should be able to export it and display everything correctly in Unity.
