How to make such a junction – a visor of metal roofing to siding?
Make it like the end part of a skylight. Flip the bottom part like a "tie," fold one edge under the shingles, and attach the other to the siding trim. Bring the edge to the end of the shingles with a slight bulge. The inside corner can be flipped over the top at a 90-degree angle to match the color of the shingles or siding.
I do this way: after installing the roof, put the wall, and in the usual version (without siding). You need to make a cutout in the wall, where the edge of the wall is inserted and caulked or plastered. In your option, you just put a J-profile, and mount the siding.