Copying should work.
What OS are you on? What version of Obsidian?
If you temporarily disable Vim Mode plugin, does Copy using the shortcut work? (This shouldn’t matter. Just testing.)
I am fairly sure that Copy and Paste are not Obsidian shortcuts, but are handled by your OS. So there is also a chance you have an app or service or hotkey manager installed that might be interfering with that shortcut.