I also bought the Jabra 65t earbuds, ended up returning them for the same reason, the sound quality on Teams was not good. I inquired with Jabra customer support, they said the 65ts were not optimized for Teams (i.e. internet phone applications), and there was nothing they could do. I replaced with a Jabra bluetooth headset w boom mic for calls, and that came with a Jabra Link 380 USB - bluetooth transceiver that provides a better quality connection than using the PC's onboard bluetooth transceiver. Audio quality is excellent. So this does point to where the problem lies.
That said, I recently used my Surface earbuds for a Teams call using my iPhone and had no problem with the audio. I seem to recall previously having the same left-ear buzz using Teams on iPhone, so perhaps they've fixed that problem.