not light blocks not barriers not any block ive seen, looks like pistons but not sure

that's a moving piston, it may not be solid but it definitely exists, it's the 2nd block of an extended piston, but it can be placed manually using commands to block players from placing blocks at a certain place without needing to use a solid block

Yea this is another block used in mapmaking, the mod shows all of these kinds of blocks.