The QuickLook function of macOS creates thumbnails in finder. You know this useful feature: When you select a file in the Finder and press the Spacebar, a preview of that file is displayed. For this purpose, the mostly reduced thumbnails are cached in a different location on the hard disk and are recorded in a database. This allows a next view to quickly reuse the previously created thumbnails.
Unfortunately, this also happens with encrypted container systems such as TrueCrypt/VeraCrypt or encrypted Apple image files when you open and use the Finder to preview them. Incredibly, this vulnerability has already been documented in 2010 and Apple has not yet implemented a solution.
SimpleumSafe uses approximately the same way for preview files. An encrypted Apple container image is created as a cache and the file is copied into it and a preview is also created.
Nevertheless, the preview at SimpleumSafe is not cached and also not recorded in the QuickLook thumbnail database. We use these feature slightly differently than the Finder to not have this security issue.
This shows us once again that it makes sense to use an additional security layer (SimpleumSafe) additional to the already quite good security of macOS with another independent software.
So: SimpleumSafe was and is NOT affected by the QuickLook security vulnerability and your data is still protected.