I think you are correct, most counties do as well. To the best of my knowledge On-x is also just a big compilation of State and County GIS maps with their own features added.
If you’re looking for an actual arcgis map you’re going to have to download shapefiles and import them. Most state resource websites will have the .shps available online. If you’re looking for and app id suggest on-x or the likes for ease of use.
Having access to arc map and knowing how to create georefrenced maps of the areas you’re hunting/hiking in and importing those into Avenza is the ultimate resource.