I have been using Lightroom Cloud version for 2 years on a PC and have never had this problem before. LR won't let me export the photos I have selected. The Export menu item is dimmed/inactive.
Do you mean the Export line in the top File menu is dimmed?
Does the key shortcut Ctrl+Shift+E not work?
Is the [Export] button dimmed/inactive?
Do you never see the Export dialog window?
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