When connected to my FM transmitter, I am able to hear audio from calls but they can hardly hear me.
Similarly, if I want to use Google Assistant, I have to shout. I believe the issue is that a microphone on the transmitter is being used as opposed to the microphone on my phone, and this microphone is bad. However, this has always been an issue, even when the device was new 3 years ago.
I can't seem to find info on the exact model of transmitter that I have, but this was the title on Amazon: Car FM Transmitter W 2.4A USB Charger, Nulaxy™ 2015 Newest Wireless Bluetooth FM Transmitter Car Kit for All Smartphones, Tablets, MP3 Players Sold by: DinoSonics
It seems like there should be a setting for choosing which microphone to use when connected to a Bluetooth device, but this doesn't appear to be an option. For reference, I am currently using a Pixel 3, however the same issue was present with a Pixel 2, Droid Turbo 2, and Galaxy S5, obviously on many versions of Android. If this is the wrong board to ask this question or if any more information is needed, let me know.