after upgrading to Big Sur 'Photos' cannot find original files

Thank you for replying. The Photoslibrary is in the pictures folder, the gist of the error message is 'original file cannot be found' and if I 'unpack' the photoslibrary there are indeed no files in the 'original' folder; photos cannot be exported and a slideshow cannot be run. A workaround to to screen grab the image which has a reasonable image but this of course is very time consuming. And I wonder whether it is be the updated Photos App that is the culprit rather than the OS upgrade to Big Sur. I also had this problem 18 months ago with Catalina and suspect it is all down to Apple scanning the images on the pretence of producing memories etc which I am quite capable of compiling myself and as mentioned earlier I wonder whether the company has ulterior reasons for such an activity namely forwarding interests to relevant companies or Governmental Spy Agencies. Have tried control-option ? reconfiguration approach and also retrieving an earlier version via time machine but neither have helped Further comments would be much appreciated

Thank you. I suspect I have never had 'copy items to the Photos library checked! I have simply imported photos directly from camera into the Photos App. But I have then been able to initially edit these photos using the Apps editing tools, view as a slideshow and gather into an Album after the camera has been disconnected from the computer. So I wonder why when revisiting these photos the App is only now asking for the originals which of course have been deleted from camera a long while ago. The upgrade was from Catalina and the photos are only backed up using time machine as a copy of the Photolibrary

Thank you. You have been very helpful.