This study has some information which is probably useful to you: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5315722/. I’ll describe the main points here and how they relate to your question.
As you mentioned in your question, some visually impaired people are able to learn echolocation to help orient themselves and recognise objects. It is also possible for sighted people to learn echolocation, so I’d say that it is within possibility that someone who is in complete darkness for an extended period could learn echolocation.
The study linked above found that the earlier in their life someone lost their sight, the better they were at using echolocation. They also found that some people were more receptive to learning echolocation. This is probably similar to how some people are better at learning how to play an instrument than others. So I don’t see any reason why you couldn’t make your character receptive to learning echolocation, although they would have to be very receptive (and determined) in order to teach themselves.
I will say that I’d find it unlikely that a person trapped in a lightless cave would choose to learn echolocation, unless it was a very large cave with lots of tunnels and they regularly explored new areas. If it was a small cave, it would be easier to simply memorise the layout. Or if they just really wanted to I guess. Or if they were hunting for food...
Also if your cave isn’t completely lightless, over a year or more their eyes would adapt to be able to see in very low light.
So overall, it is possible for a sighted person to learn to use echolocation, especially if ‘blinded’ by living in a lightless environment, but their ability and likelihood of learning will be dependent on the person and the need.