Try using Pack and Go.
In windows explorer find the top level assembly you want to copy and right mouse button on it to bring up the sub-menu.
From the list displayed pick Pack and Go.

In the Pack and Go Window set your destination folder location etc

First thin gto check is are you using the correct project (should be the project that controls the assembly you are copying)
1. Pick a location for the copy.
1. Set the options- Single path (flat file structure).
1. Pick options for libraries templates etc
2. Pick the search now button and the File Found window will populate with the files in the top level assembly.
3. The "Start" button will no intensify.
3. Pick the start button and the pack and go process will begin.
When it has finished close the dialog window.
Back in Inventor close all open windows and in the projects dialog pick Browse.
Search the folder location you specified in step 1 of the pack and go process there you will find a project.
Pick this to select it as the current project and you can begin to modify the parts and assemblies without destroying your original data.
Hope this helps
Did you find this reply helpful ? If so please use the Accept as Solution or LIKES button below.
Daren
Dell Precision 7720 + P3418HW
Windows 10
Product Design & Manufacturing Collection
Inventor 2021.0.1, Vault Professional 2021, Showcase 2017