I have been connecting my A21S to my Renault Captur Media Nav, via Bluetooth for some time with no problems.
Recently, I find that, during a call, I can hear the other party, but they cannot hear me. If I switch to my Active2 Watch the audio work fine both ways. Ditto Apple Air pods. It is not a physical problem with the car as it works fine with my wifes S20.
I have deleted the Bluetooth connection on both car and phone and re-connected - no difference.