Learn Dutch: Wij klagen over het nadeel en we debatteren erover. - We complain about the disadvantage and we debate about it.

In Dutch, you generally don't use a preposition followed by a normal pronoun (like het or dat) to refer to things or concepts. Because het nadeel (the disadvantage) is inanimate, you must replace the pronoun with er and attach the preposition to the end, forming the pronominal adverb erover.

If we were debating about a person instead of het nadeel, would we still use erover?

No. This is a strict rule in Dutch: you only use er + preposition combinations for inanimate objects or concepts. If you were debating about a person, you must use the preposition plus a personal pronoun. For example, you would say en we debatteren over hem (and we debate about him).

Both halves of the sentence translate to "about" - how do we know over is the right preposition for both verbs?

Both klagen (to complain) and debatteren (to debate) happen to take the fixed preposition over. The first clause spells it out as over het nadeel. In the second clause, we still need over for the verb debatteren, which is why it becomes part of the compound erover.

Could we split erover into two separate words in this sentence?