FLStudio's plugin manager is not up to date with the latest versions of the SDK.
This was taken from the page "VST 3 Locations / Format" in the SDK documentation:
[quote]
On the Windows platform a VST 3 Plug ...
Flstudio 20 and i had thought that everything was downloaded but when i go to scan and manage plugins it stays stuck on scanning and the ERROR pops up as shown on the screen recording. I have been trying ...