During a debug session, you can view variables in the Variables pane of the Debug tool window and inlined in your code. For stepping, the values are re-calculated on each step, which can cause performance degradation, especially in case of large structures or arrays. Meanwhile, if you do not need to explore the variables on each step, why not view them only 'on demand' to avoid unnecessary calculations and improve the stepping performance? For this, use the Mute Variables option, and CLion will stop re-calculating values for every step, letting you load them only when needed.
Mute Variables is available from the context menu of the Variables view:
When you set the Mute Variables option, values in the Variables view and the editor got hidden, and the Load link is shown instead. Use this Load link to unmute a variable for the current step - the value will appear both in the Variables view and in the editor. Note that it will not be automatically re-calculated for the next step unless you load the value again.