DVD/CD Drive no longer shows in Finder I tried to drag a DVD to  VLC app. Instead the entire DVD/CD drive just disappeared from Finder.  The drive is still there: I can play a DVD on it. But it does not show up in Locations.
Update 6 months later   I have tried two different external Cd/DVD drive's: both can play DVD/USB's but neither show up in Finder.

Note that it is enabled in the Preferences:

How can the DVD/CD drive be re-added to Finder?  I am on  Catalina with a Macbook Pro 2020.
Update Here are the Sidebar settings - showing that the External disks and CDs, DVDs, Ipods are enabled:

Another update After removing plists per the accepted answer and killing Finder (and auto restart of same) we get the external drive and CD
The first thing to try is to test the problem in a new user account. If the DVDs show up in the Finder in a new user account, then you know the problem is somewhere in the original user account's Library: a corrupt or misconfigured preference, most likely.
If the problem still persists in a new user account, then you know it is at a System level: so either a bug in the OS itself, or some weird interaction with third-party software installed in /Library, or possibly a global preference that is similarly corrupt or misconfigured.
Going back to the user-level problem: if that is the case, then you need to 'hunt the thimble': find the file that's causing the problem. You can remove large swathes of files and folder from the User Library, test, and then restore them if nothing changes, or restore half of them if it does, and so on.
Likely candidates are user/Library/Preferences/com.apple.finder.plist, and com.apple.sidebarlists.plist in the same folder. You may need to look for other potentially relevant filenames.