I would like to know what the difference between a locked and a closed version is. Can anybody help me?

Thanks Sebastian

Had the same question. To me, there seems to be no difference in usage. 

In both cases, no tasks can be assigned to that version. In the roadmap, locked or closed versions are not shown by default, but if you select "Show completed versions" it is shown regardless if status is locked or closed.

I'd like to know too.  Difficult to find documentation on the version states.

Dear all, please find the explanation here in the documentation: https://docs.openproject.org/user-guide/projects/project-settings/versions/#differences-between-open-locked-and-closed-versions

Kind regards