If you’re looking for painting more textural detail on your landscape than landscape material layers allows for, your best bet is to look into using Runtime Virtual Textures instead.
You could put planes or whatever in the world and set them to write to the RVT and paint on them with the Mesh Paint tool, and then the Landscape just uses the RVT instead of the layers.
PrismaticaDev on Youtube has a pretty good tutorial that covers some of the setup for this: https://www.youtube.com/watch?v=momc4h5J19Y