That can happen, but is not universal. My resting heart rate has been dropping (probably in lock step with my weight), it has not risen one bit since I started

That can happen, but is not universal. My resting heart rate has been dropping (probably in lock step with my weight), it has not risen one bit since I started taking tirzepatide. And my heart rate variability has been trending up, not down. Why do you suspect it changes energy expenditure?