I and my brother (both living elsewhere) have the same 'microphone not functioning' issue.
My phone:
"Huawei P8 / GRA-L09, Android 6.0, EMUI 4.0.3, kernel version 3.10.86-g9d4e5d5, Android security patch level: 1 januari 2018" -> Jami Together 20201222-01 (via F-droid)
My brothers phone:
"Huawei P8 Lite / ALE-L21, Android 6.0, EMUI 4.0.3, kernel version 3.10.86-g33ff982, Android security patch: 1 march 2018" -> Jami Together 20210205-01
My new "Samsung A71, android 10" running Jami Together 20210210-01 (and the version before that) doesn't have the microphone issue. The other party(my brother on his Android 6.0) can here me fine.