Beleriand is essentially everything that sunk into the sea after the War of Wrath. So yes that would include Gondolin and Nargothrond. In one way it's a bit of an odd origin option because of how vague it is, and how some of the other origin options are within it. On the other hand it does offer a more open ended origin story possibility if you want an elf that, say, lived in various locations throughout the first age depending on what the current state of Beleriand was and what kingdoms had been destroyed/abandoned yet or not.

I believe Ossiriand was the only part of Beleriand to not sink in the War of Wrath, and ended up as Lindon. Though I'm sure somebody will correct me there if I'm mistaken.