Hi, I was working with Unreal 5 and tried to make a mirror. So I created a translucent material and applied it to a box.
The strange thing is that this mirror only reflects the HDRIbackdrop…
The reflection is quite sharp (very good), but I would like to reflect the interior of the room as well.
Another observation is that when I look at the mirror from the front, I do not see what is behind me, but what is to my left.
https://youtu.be/iYa9rMMBNw0
I’m assuming you mean reflective, not translucent 
Did you put a reflection capture in front of it?
I tried to make good reflections in Unreal 5 with lumen reflections, planar reflection, reflection capture, ray tracing reflection… (with reflective material) and all the results were bad (poor quality or resolution).
Suddenly this material created by a Datasmith’s automatic conversion appeared, and it works like a good mirror. The problem is that it only reflects the HDRIbackdrop image…
The mirror reflects what is to its left, but the reflection is cool.
There must be some way to control the direction.
I tried to make a 360 capture with scene capture cube to create a cube map and put it in the HDRIbackdrop, but the captured image was very poor quality (many black areas, many dark spots, low resolution…)
This material is a convertion, but may be simplified with 4 or 5 nodes.
There’s a lot going on in that material.
Just a very smooth surface with a reflection capture in the scene should be pretty good. You can tweak the resolution of the capture.
Ok, you probably will need to go with planar. Not sure why you’re getting the skybox…