Quiet sound of notifications for iPhone 12 mini at maximum volume!!!

A lot of people have a problem with too quiet level of notifications/sms volume. No problems with max sound levels of rington or alarm clock, but only with notifications. Due to this, it is system software problem, because uses the same speakers. people misses sms/ whatsapp/telegram messages, the sound is too low even at the maximum volume level. Flashing in DFU like new device - didn't help. My previous iPhone SE (2016) - is loud and sonorous, my new 12 mini - quiet and a dull sound, even with stereo speakers...fix this problem, please, different forums are full of posts with this problem...if it is Apple's famous, vaunted quality...then there are no words...