I have birded in the US many times, Yucatan many times, many of the smaller Caribbean islands (Hispaniola and east), Costa Rica, Panama, Ecuador, and Chile, and all of the above with guides on single days here and there but mostly on my own. I have not done Amazonian South America anywhere, and like others I might have missed some species by being on my own, but happy birding experiences in all of those places.
One example was a recent (relatively, but well before covid) trip to southern Ecuador. We stayed in four different lodges but had guiding 2x half day during an about 2 week period (in both cases to see an antpitta).
Niels