I recently bought the Dji Mic Mini (without receiver). I noticed that the native camera app didn’t use the mic as a source when connected to bluetooth. Same with OpenCamera.
I was pretty worried and contacted the Dji Support. They told me a workaround is possible via the Dji Mimo app > connecting the device > help icon > Dji Osmo > Open liveview. Making a video from here indeed works with the Dji Mic Mini as a source.
The support told me the technical team on Dji side would look into it to try the device with the Fairphone 5. Maybe the native app also needs an update to support external mics (the fairphone 3 camera app has such an option in camera settings)?