We did not actively look for off-road when we travelled down, but we found that you could meander South following the smaller roads, but essentially, being such a narrow country, it all sort of follows the Pan American Highway. Even if you branch away, you end up being funnelled back toward it sooner or later, unless you really try to find alternative routes
To be honest, the best part of Chile for us was the Carretera Austral, South of Chiloe, back on the mainland: fantastic, but don't know what its like since the eruption of Cerro Chalten earlier in the year. So if its cleared up, and you have the time, I say boost down to there for some breath taking, less touristy views. That said, North of Puerto Montt, places such as Puerto Varas, and Villarica, and the coast South of Valdivia (although the town itself was a let down) are nice too. For camping, again, we found it harder to camp wild in Chile due to the higher pop density, but if you want a really nice place to camp, up a gnarly road, then head for Parque Nacional Radal , also known as Las Siete Tazas, East of Molina, and Curico. A lovely spot that we spent 3 nights at, purely because we had the campsite to ourselves. Can't say what its like when its crowded.
Take you time in Argentina if you can: a lovely place! Plenty of wild camping there, although the scenery is more bleak on the Pampa plains (we eventually really loved that emptiness). As cities go, Bariloche and of course, Mendoza to the northern part of your return are nice places to chill for a bit.
Rule of thumb, the National reserves in either country are worth seeing, only be sure to check what camping is allowed.
HTH and enjoy the trip.
Adventure: it's an experience, not a style!
(so ride what you like, but ride it somewhere new!)