Hi, the Mavic Mini is also my first drone, and my skill & experience was getting better and better after 3 months+.

I was having weak signal earlier especially in my residential area. During this MCO period, I have tried extensive flight test in front of my house (terrace house) for several direction.
Finally, I was manage to fly the MM to Height 120m & Distance 1500m in one of the direction only, in "AUTO" 5.8GHz channel. True, the app shows me it was on 5.8GHz but MM did fly to 1500m (although the spec said max. 500m at 5.8G).

The rest of direction couldn't reach to max of 500m, and i strongly believe due to LOS.
Bear in mind, LOS mean a straight line, signal interference will occur if there is a tree (or other object) in between you and the drone. The further the distance, the angle of LOS is reducing. Fly higher to increase the LOS angle.

what I learnt from:
1) Remote Controller Antenna Best Practices: https://www.youtube.com/watch?v=P7M9JtfVwQE
2) Use parabolic signal booster, this will significantly improve the signal. I bought from https://shopee.com.my/product/22737987/5918095680.
3) Switch my phone to airplane mode during flight.

Fly safe at home.