Problem with whitish residue on BMW 5

Hello everyone, I've noticed some whitish residue deposited on the outlets of my exhaust pipe and a few small pieces of this same whitish material on the ground. My engine also seems unstable. Does anyone have any idea what could be causing this problem on my BMW 5? Thanks in advance for your help.

(Translated from French)

The whitish residue could be a sign of coolant leaking into the combustion chamber, possibly due to a blown head gasket. This can also cause engine instability. Check your coolant level and look for any signs of oil contamination (milky appearance) in the oil. If you find any of these signs, it's important to have a mechanic inspect your vehicle as soon as possible, as this can lead to more severe engine damage. Let me know if you have any further questions or updates.