Here are some synonyms for nonchalantly:
* Casually
* Coolly
* Indifferently
* Unconcernedly
* Detachedly
* Effortlessly
* Unbothered
Examples:
* "She walked into the room nonchalantly, as if she hadn't noticed the crowd staring at her."
* "He responded to the bad news with a nonchalant shrug."
* "The cat lounged nonchalantly in the sunbeam, seemingly oblivious to the chaos around it."