Depending on data quality in the area you need, one of the many apps that use OpenStreetMap data can be a good backup option. Where I am in the US it is plenty reliable enough for highway driving.

Yes, I'm aware. And that's my default minimum starting place which works until you realize that google maps routed you through a private gated road and you need to readjust and reroute while out of cell-range. Or a large section of the road is passable only on foot or perhaps with a quad, but certainly not even a 4wd truck. Or it's convinced that you should simply "turn left!" off a cliff numerous times.

All of which happened to me just last week here in rural CA.

You do when starting a trip out of service. And sadly being a T-Mobile customer that's a good chunk of CA.

Check to see if you can download more territory.

On my car, deep in the options, is a screen that shows CONUS, and lets you draw a box around the portion you want to download.

I have a box drawn around an area about twice the size of California. Hopefully your car has enough storage for that size, too.

On those occasions when I'm out of a cellular service area, the map shows a banner reading something like "No cell connection. Using downloaded maps."