So, I was testing out the recent Beta 1.18.30.32 on Android, and I found the Deep Dark Cities using the /locate command. But as soon as I keep wandering around the City, I found Sculk growths that seem to be on air blocks, when I realise that those are Structure Void Blocks. I know this because you can walk through Structure Void Blocks when you're in Survival, Creative and Adventure mode. I also gave myself a Structure Void Block and held it in Creative mode and sure enough, there they are.
I'm no Add-on content creator myself (well, I used to, but not anymore), but I know that if you generate / spawn a structure in fresh new chunks, there will be Structure Void Blocks that clears out the blocks around the structure. I'm assuming the Devs didn't do a good job removing the Structure Void Blocks... Lol.