Fights in Final Fantasy 7 Remake happen in real time. However, the developers decided to implement the so-called Classic Mode, which makes the combat mechanics similar to the original. This page of the guide contains information related to this element of the game.
Classic Mode isn't the default combat mode - you need to activate it manually in the settings. However, you should know that this isn't a classic turn-based mode. Instead, this mode can be seen as a hybrid of two combat systems.
In the standard combat system, you perform attacks and decide when to use the ATB. Fights in the Classic Mode are still based on the Active Time Battle system. However, your characters are fighting automatically, and you have no influence on the course of the battle. The ATB bar charges during the battles. As soon as it is filled, the game activates the Wait Mode during which you can use the available skills.