Create a new material with a decal shader, choose one of
DecalWithColor (Default)
DecalWithGradient
DecalWithMask (Use this if you have a mask and want to animate the decal)
DecalWithUvMask (Use this if you have a mask and want to animate the decal)
Drag in the Base Map to the material
Create a a new URP Decal Projector found under Rendering > URP Decal Projector
Assing the material, scale and position the decal to fit. Look in QGIS for a refrence where it should be positioned. (A tool is being made for decal scale and position)
When done place them under the Data Layer Manager or Decals in the hierarchy.
Also when you have multiple decals on at the same time check the order to see if it needs changing.
To change the rendering order, go to the material and under Advanced Options change the priority.