I was looking at the live/upcoming section and tomorrow they have a place holder for men's sub 1 rings, men's sub 1: p bars etc and men's am qualifications which I take to be to coverage with commentary. I heard that Courtney kupets and Jonathan Horton will be the commentators for these. They have these for each subdivision, men and women.
The full replay of podium training is available in the replay section so I assume that replays of prelims will be as well
Note: I had to log in with my xfiniti login to get access to the app on my Apple TV. Don't know how much of the content is available if you aren't logged in but I did find this...
From gymcastic website
Full Streaming Schedule- NBC Olympics (first visit: 30 free minutes of video before prompted to login, every visit after: five free minutes of video before login prompt)
Each gymnastics session will include a main stream with commentary from Courtney Kupets and Jonathan Horton as well as live streams for each apparatus.