The Metal Frames and Braces from Supplementaries Squared have solid collision, but the wooden ones from supplementaries do not. I feel like the frames and braces should be solid as walking through them is kinda lame. I'd like to be able to use it as some sort of scaffolding, but really can't when you just fall through it.

and this means when they have no block in them

I'd argue that walking ontop of a frame is very odd considering its mostly empty and player would be standing basically in mid air. kind of an argument for why metal frames should not be solid either

makes sense, though id say at least the braces, which have beams in the middle parts of the frame, should be solid then. It also instead could have some sort of complex collision, so the frame part of the frame has collision. This is so the frame, which doesn't have the poles in the middle, could let the player fall through it or something.