I agree that you have to a some point learn how to approach problems which you haven't seen before, but almost every field I have seen, the right way is to start by copying solutions of others until you understand it and then riffing from there. My father was a professor/researcher and he said you shouldn't start a problem unless you knew what your solution was and what you expected it to provide.
In fact much of the research work I have done is see if technique from field x will apply to field y after I have become an expert in field y. Or push to edge of field y and take the next logical step. But pushing to the edge of field y almost always requires working through the solutions of the people who have been there before rather than reinventing the wheel.
But sure, if you do a first pass without a book, spend sufficient time trying to figure it out, then a solution manual is helpful if you are not getting the feedback loop of a professor.