I saw a similar thread, but thought I’d add this one - one of my SW users found that the VST3s were not found in Reaper 6.32 WinOS when packaged in their bundles (folders). They were found when you extracted the internal .vst3 and placed that into the folder.
I tested with the sample projects in SDK3.7.2 with the same result; I manually copied the bundles into the /Program Files/Common Files/VST3 as I always do. None of the sample plugins would appear until I pulled out the inner .vst3 files and planted them into the folder. This has worked in the past, so not sure what happened.
I am currently telling users that this is a Reaper issue as it happens with the Steinberg SDK samples as well, but was concerned when their latest release 6.33 did not catch it either.
Just placing this here in case anyone else finds it happening to them. If something has changed with the bundle behavior, please let me/us know. I did see the post at Plug-in Locations - VST - Steinberg Developer Help but nothing has changed that I can tell, from previous versions of the SDK. And, I’ve never had an issue with the bundle paradigm in Windows - it has always worked.
Apologies if I am missing something obvious…