Super fucking frustrating thing in Android: In Do Not Disturb mode, there's a special setting for "receive calls from: - your contacts - anyone". However also it's possible to add "Phone" and "Phone Services" to allowed apps. This won't do anything unless you ALSO set the separate flag. I've been having problems for 2 years with important calls not going through in "Do Not Disturb" mode despite having "Phone" on allowed apps. Only found the REAL switch today.
The REALLY frustrating thing is that every time I tried to set this up, I asked my wife to call me to see if I got an audible notification. I did! I then assumed it was working and I didn't need to do anything else. No wrong my wife is a "contact" so it lets her through whereas my doctor, lawyer, etc would not be pre-existing contacts and those go to voice email.
Update: No!! No the above is wrong!!! Checking "your contacts - anyone" did nothing!! Nothing at all!! I got a critically important phone call from my doctor four minutes ago and the phone did not ring!! There is literally nothing I can do to make my phone ring when I get a phone call!! My smartphone can do anything at all EXCEPT receive phone calls!!!

Here is the tradeoff of modern life:

- USE IPHONE: The corporation "Apple Inc" will control your every thought and action, cradle to grave. But you will be able to get your phone to ring when you have a phone call

- USE ANDROID: Your phone will have a problem where it does not ring when you have a phone call, and you will spend years trying to fix this but you will never succeed

There is a third option, "use Android with a custom ROM". Now you can only buy phones from Google and literally nothing will work and you will not be able to run any apps except the ones on Android. But MAYBE your phone will ring when you have a phone call. MAYBE.
Oh for fuck's sake I think this is the problem. So there's four separate switches for whether phone calls make a sound, and you have to have all four in the correct place and never do anything like flip a switch to make Signal stop buzzing at 3 AM and then forgot you did it, and there's no way to just ask the OS "Hey. I have an important phone call coming today. Can you verify you'll make any sort of noise when it comes"? No, you need to know the four switches and check at least three every time
@mcc I love esoteric computer systems I love it when the ancient tech god simply decides it shouldn't work right!!