A low RHR does not imply a lower metabolic rate, only an efficient heart stroke. HR’s link to metabolism is relative – when you raise your HR to 100 BPM (say), you’ll be burning more calories than someone of the same size/BF who has an RHR of 70 (say).
Your Garmin is most likely underestimating your calories. Based on your body metrics, your RMR is around 1,960 kCal/day; if we assume you burned 2,200, per your Garmin, this gives you a PAL multiplier of 1.12, which is too low even for someone who literally lies on the couch and watches TV for all of their waking hours. Spend some time looking through the Compendium of Physical Activities: Compendium of Physical Activities
Even desk work has a PAL of ~1.5. Try making a hour-by-hour breakdown of your typical day per the one done here, and you may be surprised by your average PAL: Human energy requirements . Even a modest average of 1.4 puts you north of 2,700 kCal/day typically.
If you’re actually eating 2,000-2,200 kCal and aren’t losing weight, it’s probably because you’ve tanked your metabolism.