How to output a postprocess material to rendertexture instead to the entire screen

Development Programming & Scripting
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Hello, I am trying to output the process material to a rendertexture instead to the entire screen - how can I do this while keep the normal screen (no stencil red manipulation)?
Here is the example: How to Create Masks With the Custom Depth Buffer | Tips & Tricks | Unreal Engine - YouTube
So aim is to have the normal screen view while outputting the postprocess effect at the same time to a rendertexture.

Thanks in advance