It’s a software problem and replacing the old iPhone for a new one, will not fix the issue. Some people already got a replacement thinking it was a faulty device.
You don’t have to cross your fingers, you have to read the messages in this thread.
I have checked all new iPhones 12 and 13 models (mini, regular, pro and pro max) in the Apple store just doing a simple test and I lost the count of how many times I’ve told it.
Settings, Sound & Haptics, Ringer and alerts volume all the way up.
In Sound and Vibration set the same sound for Ringtone and text tone.
Try with “Sonar” (you can find it in Classics) which is very loud.
Ringtone “Sonar” and Text Tone “Sonar and you will hear the volume difference.
Sonar in ringtone is very loud and Sonar in Text Tone is very low.
Again, it’s a software problem and with this simple test you can verify if the issue is still there or not and unfortunately hasn’t been fixed yet since iOS 14.1 when iPhone 12 came out.
All iPhones have this issue included the new one sent to you by Apple.