Just an update to my #4 comment:
I wish I had some idea what I was doing, but instead, I can only follow recipes and guess at things I don't know yet. I did successfully launch that Docker type map server from OpenMapTiles on my local machine and it was almost as easy as they showed in the videos found through https://openmaptiles.com/server/
https://www.youtube.com/watch?v=fJnZn1IpQHE
My only snag was not putting `sudo` in front of the `docker run --rm -it -v $(pwd):/data -p 8080:80 klokantech/openmaptiles-server` command I copied and pasted from the https://openmaptiles.org/docs/ guide.
I tried again using the JTileDownloader app with the"Output Zoom Level:" selection of 12, the "Output Zoom Levels (ex. 12,13,14):" textbox set to "8-18", option Mapnik selected and in the "Alt. Tileserver:" textbox I tried "http://localhost:8080/" which didn't work, then I tried "http://localhost:8080/styles/osm-bright/?raster#12/" which seemed to work. I transferred over the files to the phone as shown in https://unav.me/offline/ but still the offline maps just shows that pattern of an unplugged electric powercord.
I took a look inside one of the PNG files that came out of the "Download Tiles" operation using the Bluefish Editor. The contents of ~/maps/18/73677/96305.png is:
```
OSM Bright - TileServer GL
OSM Bright
```
Is that what a map tile is supposed to look like? I thought tiles were a set of graphic image files in raster format that the software loaded and stitched together as the birds-eye-window slid across the plane. I clicked the "Export TileList" button on JTileDownloader and see "http://localhost:8080/styles/osm-bright/?raster#12/18/73677/96305.png" in the list. When I browse to it I get forwarded to "http://localhost:8080/styles/osm-bright/?raster#7/42.535/-75.194" and it's showing the whole New York, USA image tile I selected during the initial set-up phase on localhost:8080.
I think I'm going to try it one more time before giving up but I'll use "http://localhost:8080/styles/osm-bright/" where I had "http://localhost:8080/styles/osm-bright/?raster#12/" before.