So I'm trying to figure out how to replicate this (picture attached). It seems pretty simple in concept, but I can't figure out how they did it. I have assumed it is based on some sort on extrusion from edge to tri, but I haven't figured out how that works. Does anyone have a clue?
For 1 edge
Since you're asking about a single triangle… Select the edge, Create a custom orientation from it:
now E to extrude, ⬆ ShiftY to lock $y$ axis (defined a moment ago by using the edge), M to merge and either A or B:
For multiple edges
You could use Goemetry Nodes to find a perpendicular vector, then maybe rotate randomly and finally merge by distance: