From facebool cubase user group:

CUBASE 9 DOESN'T SUPPORT 32bit VST's anymore???
HAHA!!! YES IT DOES!!! :D - just like 8.5, with a little trick!

As a big Cubase-fan I was very disappointed that they removed it's compatibility for 32bit-Vst's. After researching I got the following solution:

In the Cubase-program-folder you find the folder "components".
The TRICK is just to copy (and replace) the following 2 files from Cubase 8.5-components-folder to the one in Cubase 9:

"VstBridgeApp.exe"
"VstPlugManager.dll"

(please don't forget to backup the C9 components folder first)

After that let Cubase 9 rescan your PlugIns - maybe it helps to delete the blacklist-files in the Roaming-folder first.

With this little trick I'm using my Cubase 9 just the way I used 8 all the time, all the 32bit-PlugIns are now present in Cubase 9!
I don't know how it works with mac, I guess there should be a similar way to get it working there :-)

Have a nice day
This is the solution for old steinberg plugs that won't run in jbridge! At least for now.