Some time ago, I made a more visual approach for a small area:
- import the OSM data of the area into a PostGis database
- download the Mapillary sequences within the area
- import the sequences into the PostGis database
- execute a spatial query that identifies the OSM ways not covered by Mapillary sequences.
- export the result of the query to an OSM XML file
- from the OSM file create a Garmin gmapsupp file
This allowed me to display the uncovered streets with QMapShack and on my Garmin device.