When you open the baked material/texture, you need to go File > Save As > give it a shorter name. And it will show.
If I remember correctly, Unreal doesn’t show the baked out materials & textures because the file name is too long..
And then of course you need to somehow delete the original baked out materials too to clean this up. Don’t really know how since its hidden in Content Browser. It’s quite sad, this still happen in UE5.5