PVC conduit is allowed to be used inside the house or building.
You can install and conceal PVC conduit inside walls, concrete, underground etc inside a house or other building.
If you need to run wires along walls then the wires must be put into conduit for protection and PVC conduit is acceptable for this.
You can use either metal or PVC conduit when installing and running wires inside or outside.
However if the wires are concealed in the wall then there's no need or requirement for running the wires in conduit.
However it can help protect the wire from mice and other damage.
I ran all my wire inside PVC conduit inside my house walls because I had an issue with a mouse chewing into one of my wires and causing a short and almost a fire.