I had this problem earlier today and I just wanted to post it and the solution in case someone runs into the same thing.
The issue was that while using the native Quixel bridge in Unreal engine, I couldn’t export any objects, surfaces, or decals into the project. It would download the files successfully, I’d hit add to project, and it would say “exported successfully” but then nothing would be added.
The solution was that I had forgotten I had another project open at the same time. After some quick tests, it seems having any version of Unreal (4 or 5 doesn’t matter) open at the same time will cause it not to export correctly.