Instead of switching over to bluetooth versions of products you've already invested in (like HR monitors), it is MUCH cheaper to just use an ANT+ receiver (thumb drive or stick versions). Many might still have these around since they were standard on older watches that used ANT+ to send data to computers before that was done through bluetooth. If not, you can get ahold of one cheap on ebay. To get it to work you'd need to plug it into a USB to USB C cord or adaptor (also cheap if you don't have one). Older Samsung phones (S8/S9) used to have these adaptors in the box. SO...plug the ANT+ receiver into the adaptor/cord and plug into your S21 and you're good to go on ANT+.