Hi Martin,
Please refer to this post from the MathWorks Support Team for steps to install the documentation locally: How can I configure MATLAB to use the local offline documentation instead of the online documentation? - MATLAB Answers - MATLAB Central
Regarding the error that you are receiving "Something Unexpected Occurred" please refer to this link : Why do I see the error "Something Unexpected Occurred" when installing MathWorks Products? - MATLAB Answers - MATLAB Central
Additionally, consider checking your internet connection, available disk space, and user permissions, as these can also cause installation issues.
Hope this resolves your issue!