Preliminary report is at:
https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/201981/pdf
Note:
A few seconds later, the controller instructed the pilot to continue the turn to a 120° heading, but by this time the airplane had already descended to about 3,100 ft. With no response from the pilot, the controller transmitted, “November zero hotel golf, climbing?” Heavy breathing and “grunting” sounds could then be heard, and by that time the airplane had descended to about 1,500 ft and reached an airspeed of about 270 kts. The last ADS-B target was recorded a few seconds later, about 200 ft west and 350 ft above the impact location.
This sounds like it could this be a medical emergency: heart attack, stroke, pulmonary embolism, or aortic dissection, etc.