I used to use Gaia GPS extensively as they have a lot of overlays and it can be downloaded for offline use. However, the interface is not good, and they are constantly breaking things that seem to show up after you become "off grid". The final straw for me to delete the app and cancel my subscription was that the app was running 24/7 on my iPhone when it should not have been and was eating 20% of my battery daily without actually using it.
I have found the Forest Service MVUM to be extremely helpful in locating approximate locations where dispersed camping is allowed. Here is an example of a page on the Forest Service with these maps. In this case it is for the Arapaho and Roosevelt National Forests: https://www.fs.usda.gov/detail/arp/home/?cid=fsm91_058275
One thing about these maps is that the website assumes you know if you are looking for the "Sulphur Ranger District North" or the "Clear Creek Ranger Disctrict". Going in, it is very intimidating.
One tool that can make the maps more useful than just a generic PDF is the app called Avenza. They are happy to sell you all sorts of maps, but these MVUM maps are available for free. The benefit of the app is that it will use your GPS to show you where you are on the MVUM in real time.
Way back in the day I used to use an app called "Motion X GPS". This app seemed to really just be a demo of the Motion X companies capabilities and they eventually abandoned it. It was great for just being a generic GPS device, replicating the normal use cases of a handheld Garmin.
Another tool I use extensively is any mapping software/site that can show decent satellite imagery. I will look along a road marked in the MVUM as allowing camping for offshoots that can be parked on, and if the imagery is good, for a fire ring.