I just tried downloading the Cubase 12.0.52 maintenance update via the Steinberg Download Assistant, which I assume is the recommended way to manage your Steinberg installs (otherwise, why would it exist?). That Download Assistant is a bit of an abomination, but that’s a discussion for another day
Here’s the issue: During the install of the 12.0.52 update, a dialog box popped up informing me that I needed to reboot the computer to complete the install, and gave me the option to click OK to proceed with that reboot, so I did that, and the computer rebooted. After the reboot, access to my Cubase installation had disappeared - no more Cubase desktop icon to start it!
My suspicion was that that dialog box popped up prematurely (while the installer was still running in the background), so I ended up with a corrupted Cubase install.
Luckily, the full installer can be found in the Steinberg directory in your Download folder, and pulling that installer out of its ZIP file there, and then running it, redid my Cubase installation and got me back to a working state (with 12.0.52).
So, be careful not to fall into this trap - my recommendation would be to just download the installer directly and run it, and not deal with the Steinberg Download Assistant in the first place. You can find the installer here: