NO PREVIEWS! This has never been a problem before updating to 2020-version.
I gather you've just updated and now there are issues. Several things to try
1) Go to Tools (menu) -> Cache -> Manage Cache --then click on "Clean Up Cache" "Purge all local cache files"
If that doesn't work then reset your Bridge's Preferences
And if that doesn't work I suggest you uninstall and reinstall Bridge and if that doesn't work add uninstalling and reinstalling PS.
Inside tip: when updating applications and/or operating systems, things can happen. That's why I never update software or hardware in the middle of a project.