Is it technically possible to add AirSense functionality with just future firmware update for Mini 3 Pro?

No, the drone will need to have an ADSB receiver installed in it of which would put the Mini 3 Pro past the 250g weight limit.

thank you - OK, I wouldn't care about the weight, not at all ..
but I love the drone, and having that extra layer of safety from AirSense (manned aircraft nearby warning i.e.) I had with MavicAir2, I would have next question:
what is a reliable tool/android app (I use DJI RC as a controler with my M3P, so I can have my phone for sth else), to track and get warning about aircrafts flying nearby?

Hello there. Good day and thank you for reaching out. As of the moment, we do not have any information on DJI's future update for the DJI Mini 3 Pro and with regards to this matter. Kindly please stay tuned to the latest updates by subscribing to DJI official website at www.dji.com or following us on social media ( Facebook: https://www.facebook.com/DJI , Twitter: https://twitter.com/djiglobal , YouTube: https://www.youtube.com/user/djiinnovations ). Thank you.

Airsense is a bit of a pointless feature many aircraft don’t transmit and if below 120 m you should be below manned aircraft

djiuser_9oOxnoOgtGI2 Posted at 6-29 19:01
thank you - OK, I wouldn't care about the weight, not at all ..
but I love the drone, and having that extra layer of safety from AirSense (manned aircraft nearby warning i.e.) I had with MavicAir2, I would have next question:
what is a reliable tool/android app (I use DJI RC as a controler with my M3P, so I can have my phone for sth else), to track and get warning about aircrafts flying nearby?

Use an app called Flight Radar. It is very handy and if the manned aircraft is transmitting ADSB then this app will surely pick it up. The free app version works very well with the exception to a few ADs.

djiuser_9oOxnoOgtGI2 Posted at 6-29 19:01
thank you - OK, I wouldn't care about the weight, not at all ..
but I love the drone, and having that extra layer of safety from AirSense (manned aircraft nearby warning i.e.) I had with MavicAir2, I would have next question:
what is a reliable tool/android app (I use DJI RC as a controler with my M3P, so I can have my phone for sth else), to track and get warning about aircrafts flying nearby?

I use Flightradar24 to track the planes in the area,  its amazing how many fly below 400ft.

OK, great - yes exactly many planes below 400ft espacially if you operate close to the airports,
and helicopters around highways /-:

thanks guys

Bigplumbs Posted at 6-29 21:45
Airsense is a bit of a pointless feature many aircraft don’t transmit and if below 120 m you should be below manned aircraft

You must not have any helicopters in your area.  

DowntownRDB Posted at 6-30 03:59
You must not have any helicopters in your area.

Nope not in the UK

Bigplumbs Posted at 6-30 12:13
Nope not in the UK

Yeah, right.