The problem goes from the USD export setting in Blender: it converted m to cm. As mentioned in the post below Lumen does not process small meshes. Also I would add to Yaeko’s post below that in an archviz scene please encapsulate/shield the interior in black protector meshes to prevent light leaking. To deal with reflections in reflections you can use this trick. Also I recommend to triangulate large areas like walls.
Now the mirror works in Lumen context, but of course it has some artifacts. But I hope that reflections become better and better in new versions of UE5. Also materials like chrome in MRQ using Temporal Sample Count have very bad smooth artifacts.
