In "Hunter x Hunter" (2011), does Gyro appear and reborn to a chimera ant? In Hunter x Hunter (2011), does Gyro appear later on the anime as an ant? If so, which character from the ants?
Short Answer- He is a chimera ant but never appears in the Anime.

It is indeed true that Gyro became a Chimera Ant however how and when he was killed is still a mystery. While Gon and Killua were in a town after escaping from Neferpitou, Gyro was also in the same town (Not mentioned in The Anime Though). During the raid at the Royal Palace of East Gorteau both Welfin and Ikalgo identify Gyro's true identity and remember him as their King in their previous life. Welfin believes that Gyro's still alive and is determined to find him. Hence after the culmination of events Welfin, Hina, and Bizeff all depart to Meteor City where according to Welfin they are most likely to find Gyro attempting to establish a new nation. It is believed that he's still trying to rebuild his empire.
 Sources-https://hunterxhunter.fandom.com/wiki/Gyro