SUMMARY
If I put image files in a vault and set it to generate previews, it will generate the previews of those files in the user home folder which is outside of the vault (which defies the purpose, as now a smaller copy of the files is accessible without password), and will generate shortcuts to the files in the "recently used" list. Ideally, these previews should be generated inside the vault itself, and the "recently used" should only show files from the vault when said vault is unlocked.

STEPS TO REPRODUCE
1. Create a vault.
2. Put image files in there.
3. Open the vault folder in dolphin, and set it to generate previews.
4. Open some of the files by clicking them.
5. Close all files and lock the vault.
6. Go to ~/.cache/thumbnails and notice that previews are saved there.
7. Configure the applications launcher to use the old "Legacy Application Launcher" which was recently removed and which offered a tab called "History" which the new launchers might lack, and notice that the clicked files from the vault are there.

OBSERVED RESULT
Files from vaults generate thumbnails and shortcuts in user folders which are not password-locked.

EXPECTED RESULT
Files from vaults should not leave thumbnails nor shortcuts outside of the vault.

SOFTWARE/OS VERSIONS
Operating System: Debian GNU/Linux
KDE Plasma Version: 5.23.0
KDE Frameworks Version: 5.86.0
Qt Version: 5.15.2
Kernel Version: 5.14.0-3-amd64 (64-bit)
Graphics Platform: X11
Processors: 16 × AMD Ryzen 7 2700 Eight-Core Processor
Memory: 15.5 GiB of RAM
Graphics Processor: AMD VEGA10

ADDITIONAL INFORMATION