Anyone with "Corona not visible in C4D" problem - please try installing the newest build from this thread: https://forum.corona-renderer.com/index.php/topic,15602.0.html
If that does not help, select "customize" during the installation, and make sure that Corona is installed into the correct folder, where C4D is located. I am attaching screenshots showing the installation step-by-step.
It works and is visible on plugin menĂ¹, (great feature the sharpen in post-effects) but this release has changed the c4d native shaders in the reflection channel, now c4d materials appear insanely brighter (see the attachment, rendered before with the A6.3 and after with the newest build above). I have just tried to open the same file with the corona A6.3 on a different machine and if you compare the reflection are totally different, more shiny and metallic now (in speculare - blind legacy mode). I don't know if you are preparing something for the new R19 Cinema 4D release and its new shaders, or if it is something related to my configuration, otherwise could be a relevant issue.