Import: "second copy" is grey / not available

Dear all

I'm using Lightroom Classic on a HP Elitebook and am currently moving my entire picture libraries (20'000 pictures) from several different locations onto one single cloud/harddrive. I would like to let LrC do this job for me but the checkbox "creat second copy in..." is grey and unavailable to me. I just uninstalled and reinstalled LcR but nothing changed, any suggestions?

Thanks a lot, kind regards

Raphael