I thought in American prisons visitors mostly talk through glass? But maybe that's just something used in movies. Never been to an actual prison even here lol.
I'm not an expert, but my understanding is: Often, but not all the time. Depends on how high-security the prison is, and what the purpose of the visit is. Meeting with an attorney, for example, you're likely in private and there may or may not be glass.
The addition of plexiglass (for instance) was considered an unwelcome one recently in some prisons: https://thecrimereport.org/2021/07/20/captives-behind-plexig...