It’s possible uninstall at least the latest update from the Windows Control Panel (Program and Functions / Show Installed Updates / mark and Uninstall). I don’t know if it’s possible to step back more than that, I have not tried it.
However, you can always uninstall Cubase entirely and then install it again from here:
https://www.steinberg.net/index.php?id=14935&L=1
At the bottom of the page you have the Full installer, and above that all update files, including 10.5.12. Unfortunately, the Full installer is not just Cubase itself but also contains the entire sound package, so it’s 20 GB (maybe you have a backup on your disc drive?). (This was changed from version 11, but for 10.5 it’s still like that).