I found the details. Here's what Aaron Rodgers said about Mike McCarthy's offense in Pittsburgh:
Rodgers called the reunion "surreal" and expressed major comfort with the system, saying:
"I spent 13 years in [McCarthy's offense]. It's stuff that we used to run, but he's just called it something different now."
(from the Aaron Rodgers page, citing Steelers' Aaron Rodgers on familiar Mike McCarthy offense: 'It's stuff that we used to run')
The key point: McCarthy's offense is rooted in Bill Walsh West Coast principles — timing-based, option-heavy concepts with names like "Dragon," "Lion," and "Hank" for quick game, plus "Tex Coast" concepts like four verticals for deeper shots. Rodgers already knows the core plays from their 13 years together in Green Bay; the terminology has just been rebranded. That continuity should significantly reduce the learning curve for a 42-year-old QB in his final season.