We are sorry to hear you are having trouble using keyboard shortcuts for copy and paste in Adobe XD. In addition to what Italo has suggested, please also check if you've the latest update to your graphic card driver.
I have the same problem from time to time, the only software that this happens is XD, when this starts doesn't work in any file. Close all the instances and reopen fixes for a time, but starts again after a few hours, sometimes days.
I have the latest driver, latest XD, latest windows, and everything.