I can see that my colleagues have already answered this same question in the RadGrid forums, so I will close this thread. For your convenience, I give you the information from the other thread here as well:
it is a known problem that client-side hide/show of columns does not
work on Safari for Mac with the current version of RadGrid. The issue
is already logged in our bug-tracking system and hopefully our
developers will address it for the next release of the controls. Please
excuse us for the temporary inconvenience.
the Telerik team