Couldn't update catalog and Error database disk image is malformed

I've seen some posts about a bug on Lightroom Classic, where we try to open a Catalog that was built with an older version, and when it tries to update the Catalog an error message appears : 

after reading your posts and understand what could be wrong, I uninstalled the version 11 and have reinstalled the version 10.4. After this, Lightroom tried to open the Catalog, but another error message appeared:

What can I do more to recover this Catalog (there is a lot of work inside this Catalog and if I can't recover it I'll lost all the work done).

note: this Lightroom is installed on my client's computer.

Thanks in advance.

Carlos Barbosa