I understand how tough it is to find a good de-esser for black metal screams in Cubase. I've been in the same boat, and it's not easy with just free plugins. The trick is to get something that controls the sharp 'ss' sounds without messing with the scream's power.
I've had good luck with the Voxengo Deft Compressor. It's a de-esser and good at focusing on those high, harsh sounds. Plus, it's easy to use, so you won't have to adjust things forever.
By the way, I recently checked out https://faqaudio.com/t/cubase-13/30 and saw some stuff about Cubase 13. They've got new tools that might help with your music, especially the Vox Comp, which is made for working with vocals.
