"Use TeraCopy as default copy handler" cannot be selected in Preferences

In the preferences the option "Use TeraCopy as default copy handler" is greyed and cannot be selected. On my old PC this worked with V 2.3. On my actual new installed PC with Windows 10 it does not work. Tried it first with V 3.6 and then with V 2.3. Both have this option greyed out. Any idea what the reason for this could be (portable installation?)