"we have sth in german grammatik" O yes! And one topic is capitalization of nouns ... another one is punctuation, where is written that after commas and periods has to be a space ;) Er hat ein Kind. Das Kind ist sehr hübsch. Das Hübsche hat mir gesagt, dass ... Yes, this nominalisation is possible, but you have too be careful. In your example 'das Hübsche' doesn't fit well. If it's about a woman, it would better fit (die Hübsche). Here you can find some examples and hints how and when to use these nominalisations: https://easy-deutsch.de/en/adjectives/adjectives-as-nouns/