Each generation iPod touch has a different latest iOS available for it. This is important because not all games and apps will run on older versions of iOS. Please research what games and apps will work for you before purchasing.
6th generation iPod touch: iOS 12.4.5
7th generation iPod touch: Newest iOS
iPod touch (7th generation)
Navigation: Multi-Touch display
Capacity: 128, 256 GB
Model number and date introduced: A2178: May 2019
iPod touch (7th generation) has an 8MP camera and FaceTime HD camera.
iPod touch (6th generation)
Navigation: Multi-Touch display
Capacity: 16, 32, 64, 128 GB
Model number and date introduced: A1574: July 2015