On Kid3 3.9.3 on Windows, OggFlacMetadata is not listed in the Plugins tab of the settings.
STEPS TO REPRODUCE
1. Start Kid3 3.9.3 on Windows
2. Open menu item Settings/Configure Kid3...
3. Got to Plugins tab
OggFlacMetadata is not shown in the Metdata Plugins & Priority list.
OggFlacMetadata should be available there.
Qt Version: 5.15.2
The reason for the problem is that liboggflacmetadata.dll is built with libssp-0.dll, but that DLL is missing.
A fixed version 3.9.3-1 is available on https://sourceforge.net/projects/kid3/files/kid3/3.9.3/kid3-3.9.3-1-win32-x64.zip which is identical to kid3-3.9.3-win32-x64.zip, but additionally contains the required libssp-0.dll file.