My Cloud is now an expensive brick - please help

Have you tried SSH?

I fear apt-upgrade may already have voided the terms of WD’s warranty. Whether those terms are fair, since:

I) SSH is provided
ii) apt-upgrade is provided
iii) there’s no ‘using SSH may void your warranty’ warning in the user manual

is another question… But I would think opening the case would void your warranty. To be sure, ask WD.