Is it possible to use a Bluetooth earpiece while using a microphone plugged into the headphone Jack?
After a fair amount of testing on my Samsung Galaxy Note 9, using server different apps, I have discovered that it is not possible to use a 3.5mm jack microphone in conjunction with Bluetooth headphones.

Instead I had to use a 3.5mm splitter cable (widely available online) and connect my microphone and regular 3.5mm jack headphones.