You could use a SceneCapture 2D, which is like a camera you place in the scene that outputs to a realtime texture.
Basically you create a SceneCapture2D component in your scene, and then a RenderTarget somewhere in your asset folders, the movies folder for example. In the rendertarget you assign your SceneCapture 2d camera, after which you can use the rendertarget in a texture sample in a material.
You can find the scenecapture2d in the upper left corner of your screen, the render target you can find by right clicking like you would if you made a new material, and then navigating to materials and textures.
The scenecapture has its own page in the documentation:
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