As it says in your screenshot "Select any driver to revert it to a previous condition" - you have to first select a driver(s) for restoration before the button becomes active.
There should be a tickbox to the left of each driver name.
See this article for more info on reverting drivers if something has gone wrong with a driver update:
<div class="ipsQuote_contents ipsClearfix" data-gramm="false">
<p>
</p>
<ol start="3"><li>
Select the checkboxes next to the driver categories and or the drivers you want to revert.
</li>
<li>
Click<strong> Revert Selected</strong> to begin the process of reverting the chosen drivers
</li>
</ol><p>
</p>
</div>
</blockquote>
<p>
</p>
</li>
I've never used the Driver Updater myself, so never had to use the recovery option, but from the support article I think the tickboxes should be there?
That may depend on if you have the latest CC version installed?
@Dave CCleaner any insight on this further than what it says in the FAQ article?
If you continue having trouble after exhausting the advice in this article, please get in touch with our support team by using the Contact Us form linked at the bottom of the article, or by emailing support@ccleaner.com directly so that the matter can be looked into further.