I think parts may be available for cheap now… than taking my route… when it happened to me … i couldn’t find anything for less than 100… dealer gave me quote for 350…
I used dirty way to fix it and keep it together… I used one inch washers two and 5/16 4inch bolt (full thread) to keep the plastic together and made cut the washer on the edges in V shape to run wires… in my case i had to keep the broken plastic together… this did the job… so far it is keeping it together… i’m searching for photos i couldn’t find… will share when i find it.
Here is the link on fixing it Buick encore side mirror assembly broken into two pieces - mirror part broken from the part attached to car