2016 Volvo XC60 - coolant leak?

I have a 2016 Volvo XC60. I drove the car and stopped with engine running to throw out trash as I was leaving home. The message on dash said “Engine coolant low. Drive safely.” I had coolant levels checked and hardly any was missing. Some coolant was added to Max Level. The message went away. Is there a leak somewhere or could sudden braking cause fluid to slosh and cause the warning to come on.

Difficult to say without a hands on look at your vehicle. At five years old it is likely due for cooling system service. At that time they can pressure test your system and check for leaks.
In the mean time, be sure to watch your temperature gauge.