C172 pilot reported loss of engine power during cruise resulted in an off-airport landing.

Narrative

On the morning of my shift; I was informed that Aircraft X had a squawk noting that at 2700 RPM the tachometer was not indicating a red line. I reviewed the squawk to confirm the issue; then proceeded with my preflight.I began by checking the weather; determining the winds; and planning a departure to the south on Runway XX. My plan was to climb to approximately 2000 AGL to test the tachometer. The preflight inspection and run-up were both normal.I departed Runway XX at full power with no abnormalities. The climb-out was uneventful. At 2000 AGL; I leveled off at full power to accelerate the aircraft and verify the tachometer indication. As the squawk reported; the tach did not display a red line at 2700 RPM. I turned back toward the airport and recorded a video of the tachometer for maintenance.Afterward; I performed a 180° turn and briefly considered practicing a power-off stall before returning. I reduced power to idle and conducted the setup for the maneuver. When the stall horn activated; I applied full power for recovery; but I did not hear the engine accelerate. The tachometer appeared to indicate only 2000-2200 RPM. I attempted cycling the throttle and enriching the mixture; but neither produced any significant change--only about a 200 RPM difference between idle and full power.Recognizing that I could not maintain altitude; I prioritized aviate; navigate; communicate. I maintained full power to preserve what thrust was available. I considered performing the engine restart procedure but chose not to; as the engine was still running and I did not want to risk worsening the situation.I selected a suitable off-airport landing site on a pipeline just south of ZZZ1. I made a radio call on XXX.XX; and another pilot responded; advising that he would contact maintenance for me. I conducted the landing as a normal off-field landing and touched down safely. After stopping; I shut down the engine and exited the aircraft.Following the incident; maintenance conducted an inspection of the aircraft. It was determined that the throttle control cable had become disconnected; which prevented the engine from producing full power despite throttle input.