In some states, yes. Though it's impersonation and harassment that's illegal rather than simply being racist.
In general, impersonating someone—online or offline—is unlawful and can result in criminal or federal charges if it involves false representation with certain consequences. Individuals may also face civil liability for impersonating someone online.
Being racist on the internet using a troll account is an arrestable offense??
In some states, yes. Though it's impersonation and harassment that's illegal rather than simply being racist.
https://www.minclaw.com/social-media-impersonation/#:~:text=Impersonating%20someone%20on%20social%20media,or%20otherwise%20negatively%20impact%20someone.
Here is a link about his arrest:
https://www.houstonpublicmedia.org/articles/news/fort-bend/2024/06/13/490615/candidate-for-fort-bend-county-commissioner-taral-patel-arrested/