For a very long time garmin has made their Heart Rate Monitors Ant+ only. Many speed/cadence sensors are also Ant+ only. There are only a few different ways that you can bridge Ant+ to Bluetooth so that it will be compatible with Zwift. If you run Zwift on a computer, there is a pretty easy solution to this. An Ant+ dongle will allow Zwift to pair to devices through Ant+.
The first and most popular solution is to get this device: https://store.npe-inc.com/cable-connect-ant-to-ble/. It is not very cheap, if it is just one device, like speed/cadence sensors or a Heart Rate Monitor, I would recommend just getting a new sensor that already has bluetooth built into it. This device works very well to bridge to Zwift. It is probably the easiest way to bridge the gap. 4iiii also sells a heart rate monitor that can bridge ant+ to bluetooth that is very accurate in monitoring your heart rate.
This second solution is one that I discovered when I had this issue. PM5 head units on Concept 2 rowers can also bridge Ant+ Heart rate monitors to bluetooth. I wrote about this in this article: https://www.pursuitcyclingforkids.com/how-to-use-concept-2-with-zwift. This should work to bridge the gap. This is a pretty long process just to get a heart rate monitor to pair with Zwift, which is why I ended up just getting a new heart rate monitor.
Thanks for reading and I hope that this solves any issues that you may be having! If you know of any other ways, or if these solutions don\’t work, just leave a comment below!