In “The goal is hard to reach,” “hard to reach” is adjectival and modifies the goal.
The goal is hard to be reached? No good. Neither formal nor informal. No good. “Hard to be reached” could even clumsily imply “being reached is hard.”
“The goal is too hard to be reached” would work. (“Too hard” internally modifies the verb “reach,” but the entire phrase “too hard to be reached” still modifies “the goal.”)
“The goal is not easily reached/reachable.” Grammatically OK.
Stick to “The goal is hard/easy/impossible… to reach.”
The goal is to be reached. OK, but it means something else.