Hello, I was modeling in Houdini, but when exporting the .fbx to use in Unity, it only exports a single mesh. How can I keep the different parts of the model separate so I can use it as a digital twin in Unity?

Do you have an example file you'd like to be imported into separate pieces?

I can think of a couple of options that may be helpful. When importing an FBX into Unity, you can right-click and create child objects within the imported FBX into their own prefab_variants.
You may need to disable Weld Vertices in the FBX file in Unity.

You could go further and create an Editor script that automatically splits an FBX file into separate prefabs_variants.