Here is the area...

If it is high resolution, you may need to reduce the resolution a bit as well as waiting for the grayed out image to gain full color.

Vinca is not native. Why not do bearberry? Or plant something like mountain laurel?

Because in Wi you cannot automatically assume acidic soil.

Actually in New England you cannot automatically assume acidic soil. One of the great revelations (to me) in William Cullina's books is the number of New England natives that are described as preferring neutral to alkaline soil.

I have a vinca covered backyard hill. I've been weeding this beast for 41 years. I don't know how to avoid the weeds, maybe landscape fabric between the plants?

Landscape fabric just makes weeding more difficult. Try a combo of weeding well and not allowing anything to go to seed, maintaining a good layer of mulch below the Vinca, and if you want to prevent reseeding, try using appropriately timed Preen.