Vivoactive 4 HR rate / Taxc Flow / Mac book

Hi can anyone kindly advise I’m on the right path here.  I have a Vivoactive4 watch and just bought Tacx Flow Smart.  To get my watch HR accessible on Taxc app I believe I need an ANT+ USB dongle for my Mac.  Is that correct?  And does the Garmin ANT+ USB dongle support Vivoactive4 since not listed in the supported devices?  Or do I need some other setup?  Thanks in advance.