Is dhikr (remembrance of Allah, such as Istighfar, Tasbeeh, etc.) accepted while driving or listening to someone speaking? Is it permissible to perform dhikr with the heart without moving the lips? And which is better: raising one's voice or lowering it?

The remembrance of Allah has three states: with the heart and tongue (the best), with the heart alone (second degree), and with the tongue alone (third degree). It is not a condition to comprehend the meaning of the remembrance when it is done with the tongue, but it is more perfect for the heart and tongue to be in agreement. It is permissible to remember Allah with the tongue alone or with the heart without moving the lips. There is no harm in raising one's voice with it as long as it does not disturb others, and it is better to do it silently because it is more conducive to humility and further removed from ostentation.