GAIA GPS for me, with the USFS and public lands layers. GAIA now has an Overland layer which combines most of the manual toggling before into the bits you need: USFS, BLM, UMVM maps, and their base topo map. Then it’s about pointing the rig somewhere and exploring.
iOverlander can be okay in a pinch/necessity but I find those are very hit and miss and because of its popularity, busy or just super random.
I have OnX, but don’t like it as much — great for finding trails, and subsequently, camping, but I’ve long used GAIA and find it’s level of detail really good.
A lot of spots can be sort of gleaned or approximated from small hints in social posts or YouTube videos, then going to a satellite map or GAIA to poke around.