If it's not bioavailable, then it's not going to affect homeostasis so I'm genuinely not sure what your concern is.
This has been studied since the 70s and there's currently no data to suggest it affects homeostasis as far as I'm aware.
To put it simply, if you're healthy and your bile ducts aren't fucked from drug abuse or whatever else, then the small amount of copper in GHK-Cu isn't going to pose a risk. It's so far below the maximum tolerance for copper. Any excess copper, whether it's bioavailable or chelated, or whatever else, is going to be excreted via the natural systems that handle it. Bile ducts.