On February 20, 2021, about 1700 eastern standard time, a Cessna P210N, N210GE, was substantially damaged when it was involved in an accident near Bartow, Florida. The commercial pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, the airplane’s engine oil had been changed earlier during the day of the accident. As the airplane climbed through 5,000 ft mean sea level (msl) on the accident flight, he heard a “clicking” sound every minute and noted that the sound occurred simultaneously with a “pegging” of the analog oil temperature and oil pressure gauges to the right, and the ammeter to the left (full discharge). He checked the circuit breakers and fuses, but did not observe any anomalies. The airplane was at 14,000 ft msl over Gainesville, Florida when the pilot decided to return to the departure airport instead of continuing the flight over mountains at night with a possible electrical problem. The “clicking” sound subsided while returning, and the pilot subsequently extended the landing gear, flaps, and speed brakes. He looked out the window to verify that the landing gear was down but did not look at the gear indicator light on the instrument panel. The airplane touched down on the runway, and the pilot reported that the tail seemed to “fall out” from under him. The airplane leaned to the left and continued in a straight path to a stop. He pulled the mixture control, shut off the master switch and magnetos and egressed. The pilot then walked around the airplane and observed that the nose landing gear was properly extended; however, the two main landing gear had collapsed, resulting in damage to the horizontal stabilizer, left wing and fuselage. Examination of the airplane revealed that the landing gear hydraulic fluid reservoir was empty. The reservoir was filled with hydraulic fluid, and the airplane was placed on jacks in preparation for a landing gear swing. The electric master switch was turned on and the landing gear handle was moved to the up position. The landing gear retracted normally, and the motor shut off when the landing gear was retracted and locked in position. The landing gear handle was then moved to the down position, and the landing gear moved to the down-and-locked position with the green down and locked light on. A drop of hydraulic fluid was observed on the ground under the left main landing gear after the landing gear was lowered. The inspection panel was removed from the left main landing gear down lock actuator and hydraulic fluid was noticed leaking from the actuator.