The issue is that if you are on your phone doing things, then you can go on silent mode and still see the notification of a call coming in without the sound (and decide if you want to answer it). If you're not looking at your phone when it's on silent mode, then you won't see that a call has come through, be it from one of your designated emergency contacts or from anyone else.
The advantage of DND mode is that you can make the phone be silent except 1) for calls from your designated emergency contacts, 2) from any contact that tries to call you three times in a row. The disadvantage of DND for some people posting here seems to be that they want at least a vibration alert, not complete silence, during DND mode, for all contacts (not their approved emergency contacts).
And I have highlighted the issue that VoIP calls coming in from apps (such as my dual-sim app), are problematic since they create sounds in DND mode because the phone does not categorize those sounds as call sounds but as media sounds. So DND mode does not work if you want to allow emergency contact call sounds, and do not want sounds coming through from certain media apps (such as calls coming through on my dual-sim mapp) but want media sounds from other apps, such as Netflix. Silent mode is not sufficient since it blocks all unwanted sounds (I don't get the sound alert from an incoming call on my dual-sim app, but I do get the sound I want to get from Netflix) but this also means that emergency contacts' calls (or calls made by the same number three times) do not produce any sound (to wake you up in an emergency in the middle of the night, for example.
I found a temporary workaround which is not ideal, but which helps. Here is what I am doing, in case it can help others. Since my dual-sim card device is communicating with my S10 via Bluetooth, I ran a Bixby routine that tells my phone to deactivate bluetooth at a set time at night during bedtime and that it reactivates it at a set time in the morning when I wake up. That way, I go into DND mode at night and calls from my emergency contacts can get through/make a sound, but my dual-sim app is not going to be connected and making sounds to wake me up if I receive a call on my overseas number while asleep. This works for me because I do not use a bluetooth speaker connected to my phone to play music or anything else during those bedtime/sleep hours, so I am happy to have bluetooth turn off automatically at night and have it automatically come on when I wake up and re-connect with my dual-sim card device to let any calls through again.
