minecraft-java-edition
According to the wiki, mobs do not spawn in water or lava, or in a block that has higher light level than the limit for the respective type of a mob. However, it appears that mobs also cannot spawn in pressure plates, and that seems like a an exception to me, since pressure plates aren't solid.
Are there any other non-solid blocks that prevent mobs from spawning in them (not on them)?
The rules for "normal" spawns do not seem to apply fully to Mob Spawners. A dungeon with a completely flooded floor is not safe. Apparently the random block in the 9x9x9 cube can be air.
Here's a flooded dungeon, and here's the same dungeon after I turned the difficulty to Easy (and removed the torch). The spider spawned in the water and climbed up to the ceiling.
Edit: Test repeated with source blocks, and a torch for better visibility.
Mob traps built close to the sky limit have been known to end up not being completely loaded by the engine in some situations. The way to test for this is to open the F3 screen and look at the 'lc' value. This number is the highest Y-level that is currently loaded. If it's lower than the top of your mob trap then you would need to add some blocks above the trap to force the entirety of it to be loaded. This youtube video shows how you can fix the problem if it happens
It's also worth mentioning that the high altitude mob traps are (all other factors being equal) always going to be at least somewhat slower than low altitude mob traps simply because there ends up being more blocks for the spawning algorithm to check
Best Answer
Yes, all the blocks that are non-full and have a hitbox that touches the bounding box of the mobs will prevent mobs from spawning in them. This includes Carpets, Slabs, Stairs, Daylight Sensors, Redstone Repeaters, etc. As an exception (as you said) Pressure Plates also prevent mobs from spawning, maybe in order to make mob spawning harder, but this was not the case before the Minecraft 1.9 version.
They will spawn in most non-solid blocks, regardless of being full or not. This include Grass, Flowers, Sugar Cane, etc.