Carnap's statement is false, humans find all sorts of non-verifiable beliefs and experiences cognitively meaningful. Dreams, religions, ancestor worship, coincidences, hypothesises, potentials, the future, stories....
Carnap is falling into the fallacy of scientism, in neglect of anthropology, sociology, fiction writing, and any number of other humanities subjects and activities.
Humanity being interested in unknowns and unverifiable understandings and forms of belief is vital to having a broad human experience which is vital to having a good life, and a good understanding of humanity.
We are not a solely rational species.