No, HOI4 is not a turn-based game. This game is real-time with pause and speed mechanics, which can help you slow down or speed up the game when you need to.
However, there is a specific game feature called ironman that is related to the time and way the game is played. This feature is called “ironman” and you can select this mode when you start a new game.
What is the ironman mode in HOI4?
You can play indefinitely, but you only have one save game file from the current game. That means that you can’t save the game before major decisions. All you can do is to shut the game down and start where you end last time.
Why play ironman mode?
Because this mode is the only way to get Steam achievements from Hearts of Iron 4.