Necro-posting this, since I was looking for a way to create a perfecct 1:1 reflection with lumen and all, and I found out the mirror demo project posted up here. I opened it with unreal 5.4, but I think it was made with unreal 4.8 or something old like that, so you need to fix it a bit.
Open the Mirror BP and create a SceneCaptureComponent2D in the mirror blueprint and reference that instead of the default “SceneCapture” variable. Remember also to set the same render target in the new SceneCaptureComponent2D. Then just swap the two set actor location and set actor rotation with a compatible version with the newly created SceneCaptureComponent2D (drag a pin from the variable in the graph and search for “set world location” and “set world rotation”), and then, in the scene, delete the original scene capture actor. Now everything should work.
(Sorry for the spaghetti code :D)
There’s a little misalignment at the bottom of the mirror as you move, and the movement is a bit jittered, but I think that could be due to some offsets between the scene capture and the mirror plane, or the use of world instead of relative location and rotation. I should investigate more, but for now it’s good enough for me! Good luck!