The same here. It happens once a month on average. Not very often, but still annoying. It happened 2 or 3 times in the middle of the night, 100% loud (despite the phone was muted) and without any information on AOD screen. After opening the case, the ringing ceased.
Bingo! That was it! I'm using Miband 6, which is paired with my Samsung. Since I was using a simple screen tap to enter Miband's menu, I accidentally switched various options in my smart band while sleeping just by touching the screen. Sometimes it was just "find my device".
I have changed the way of entering the menu from "tap" to "swipe", so my phone's loud alarms shouldn't happen anymore.
AshS21, great thanks for your advice!