I wish I could have just powered the dash cam from the mirror as well but Garmin needs a 3-wire power module to automatically switch between driving mode and parking mode. This module wouldn’t fit behind the mirror. So I ran the wire behind the passenger side door seal down into the fuse box located at the passenger footwell.
Mirror tap was very easy, I used the thinner prongs and got accessory power from the black and green wires. Counterintuitively, the black wire seems to be positive, go figure.
For the dash cam power module, I found two 20A fuses that are “spare” according to the manual. They are:
#4: permanent 12V
#37: accessory 12V
Ground was easy, there is a bolt just at the edge of the carpet.
Main goal was to keep these units out of sight and I’m pretty happy with the results!