Indah itu baik
"Beautiful is good" Itu is functioning as adalah/ada here but how do i know that this is so? The translation could also be "That beauty is good.", couldn't it?
An Indonesian native speaker actually criticized this sentence. It's grammatically incomplete and incorrect. https://hinative.com/questions/17963856
"Indah" functions only as an adjective, and adjectives alone cannot be subject of sentences without being preceded by verbs (i.e. turning into gerund).