We're sorry about the trouble with Lightroom Classic. Would you mind sharing the exact version of Lightroom Classic you're using along with your computers macOS version? Since when are you seeing this behavior? Do you have sync enabled in Lightroom Classic & is the app syncing any images while you're using the app?
Please ensure that Lightroom Classic has the necessary permissions on your Mac by following the steps suggested below:
1. Go to the System Preferences for your Mac, then Security and Privacy, then select the Privacy tab.
2. Then select Accessibility from the list to the left & check if Lightroom Classic is added to the list with a check mark in front of it.
3. If Lightroom Classic is not a part of the list, please add it by unlocking the window first using the lock at the bottom left, then clicking the + icon & navigating to the Applications folder.
4. Also, grant permissions to Lightroom Classic under Full disk access located in the same list as Accessibility.
5. Once done, restart the Mac & check if it helps.
Image files synced to the the Adobe Creative Cloud storage from Lightroom Classic Collections are Smart Previews and not original image files and do not utilize any of your storage allocations.
Image files from your mobile devices, Smart Phones and Tablets using Lightroom Mobile or Lightroom (cloud-based) application on your computer do sync original image files and will utilize your storage allocation, this is referred to as Lightroom ecosystem (cloud-based) and have a separate forum.