Nothing appears in the "Select Volume" box when trying to run "Erase Free Space"

There is no hard drive for me to select. Not sure what to do. Can't find any answers. Would appreciate some help.

Running Big Sur 11.1

Thanks. 

Is your drive an SSD?

Most modern MACs ship with SSD's installed as standard.

CCleaner for MAC 'Erase Free Space' will not wipe SSD's, it is not needed.

CCleaner for MAC used to tell you that if you seleted an SSD to wipe.

Even MAC's own Disk Utility will not let you Secure Erase (wipe) an SSD, again because it is not needed:

https://support.apple.com/en-gb/guide/disk-utility/dskutl14079/mac

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		Secure erase options are available only for some types of storage devices. If the Security Options button is not available, Disk Utility cannot perform a secure erase on the storage device.
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		Note: With a solid-state drive (SSD), secure erase options are not available in Disk Utility. For more security, consider turning on FileVault encryption when you start using your SSD drive.
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Yes. I have a 1 TB SSD Flash Storage. When you say I don’t need to wipe what do you mean? Once I empty my trash the files are gone forever?

Yes, and then again not quite.

It's all to do with the way data is written to an SSD, which is different to with a HDD.

PS. Even this article is 5 years old and SSD technology has moved on since then:

https://www.howtogeek.com/234683/why-you-cant-securely-delete-a-file-and-what-to-do-instead/

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		With modern solid-state drives the drive’s firmware scatters a file’s data across the drive. Deleting a file will result in a “TRIM” command being sent, and the SSD will eventually remove the data during garbage collection. A secure delete tool can tell an SSD to overwrite a file with junk data, but the SSD controls where that junk data is written to. The file will appear to be deleted, but its data may still be lurking around somewhere on the drive. Secure delete tools just don’t work reliably with solid-state drives. (The conventional wisdom is that, with TRIM enabled, the SSD will automatically delete its data when you delete the file. This isn’t necessarily true, and it’s more complicated than that.)
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In simple words data should not be recoverable from a SSD following normal deletion.

But it <em>might</em> be with <em>forensic</em> recovery tools. (We are talking government agencies and the like, not the sort of thing a normal user would have access to).

There was also the issue with earlier SSDs that a secure erase would use up the limited number of write operations and so shorten the life of the SSD.

If you are worried about data (deleted or not) on a SSD then as that article (and the Apple one above) says you should use file encryption.

(No guarantee that a forensic agancy couldn't crack that encryption of course).

PS. You will see tools advertised that will state they will 100% securely delete SSDs, reputable tools won't make such a claim.

There is only one way to make sure that nothing could ever be recovered from a drive, any type of drive, - physically destroy the drive.