I'm a Windows user, so not sure... but try this, load the object by either highlighting it (single click) and then use the check marks at the bottom of the library to load the item, or try left clicking on the item and dragging the image to the interface window. If you still get two files, appearing in the scene then something weird is going on there. If you were a Windows user I'd suggest that single click might be double clicking (maybe a mouse problem). Does this happen in any other programs? Try to check your mouse properties in your Mac control panel. Hopefully a Mac user will be able to provide more help :)

Edited to add this link

https://support.apple.com/en-us/HT202319

Maybe it's the Double Click speed setting? Just guessing...

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