i am having the same problem and i tried all the suggested steps and it still isn’t showing either stereo room or the other plugin that was offered bundled with studio one.
the first time after i installed the plugins i did not have iLok running and when i opened studio one it told me it wasnt running (error message) while loading.
so i closed studio one, got ilok running with activated plugins, and restarted studio one. no go.
then i came here, did the recommended steps and still not working.
any tips? i saw an article about ‘reseting plugin blacklist’ for studio one, but it appears it references an older version and did not apply to studio one 3.