SUMMARY
When you install a Global Theme and then delete it, when you go to Discover "Installed" page it is still present. If you delete it, it re-appears the moment you re-open Discover. Even worse is that when Discover says that it is still "Installed", it re-appears "partially" (what i mean by partially is that it won't get installed as a global theme, but just as a Window Decoration and as an Application Style if i'm not mistaken) in the System Settings themes. Even if i delete those themes manually from the System Settings, it is still present on the Discover "Installed" page.

STEPS TO REPRODUCE
1. Install a global theme from System Settings
2. Delete the same theme from System Settings
3. Check on Discover that it is still installed
4. Delete it from Discover
5. Check on System Settings that it is still present on certain theme sections
6. Delete the 3rd party themes from System Settings

OBSERVED RESULT
It is still installed on Discover, even if you try to delete it again from discover, it will still re-appear on System Settings.

EXPECTED RESULT
It isn't installed either on Discover or System Settings, it should disappear the moment you delete them from one or another.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: CachyOS Linux
KDE Plasma Version: 6.5.5
KDE Frameworks Version: 6.22.0
Qt Version: 6.10.1

ADDITIONAL INFORMATION
!IMPORTANT INFO:
I solved this bug by manually deleting ~/.local/share/knewstuff3/aurorae.knsregistry and another file i don't exactly remember the name. Then i deleted the themes manually from ~/.local/share/aurorae, and they wouldn't appear anymore.