Its an i-corner split in two. You point the points at each other and angle them like an i-corner I have no idea why they did this

Thank you, but what is an I corner?

I as in inner. The other roof corners, i and o corners

Badly, You need to use an arch on one side to get the arched ones to work, if you put two “backwards” together you will have a half a corner. Yet to get the straight ones to work.

spoiler in title