When limiting access to certain topics, you will likely want most of your topics to remain Unlimited Access and only a handful of them to be Limited Access. The easiest way to check that you have the correct topics set for Limited Access is by using the filter at the top right of Content Hub.
First, expand out your Content Hub by using the Expand All icon:
Then apply the filter to Limited Access. This will reveal only your topics set to Limited Access, and you can then update the access status of any that you need to change in the usual way, by clicking the padlock icon.
If you want to check the Unlimited Topics instead, then simply change the filter to Unlimited Access.
For more detail on how to use the Access Level feature see this article.