It's probably bixby I'm pretty sure you can turn it off in settings if it's annoying you or you could silence her by going to sound and at the end of all the notification noise and system noise it will have a weird b turn that all the way down hope this solves your problem
I found this similar problem, I have exactly the same:
"A couple days ago I started hearing a womans voice at random times, like I had butt dialed someone, but I could Identify where it was coming from. Then while I was scrolling on my phone I hear something something "time". Finally in the middle of the night when everything else was quiet I hear it clear as a bell. A robotic female voice saying "it is time". No notification. No background apps running. I've done a few things to check those things and can't find anything. It is slightly annoying. But more so, creepy AF. Any help would be appreciated."
Thanks for the suggestions. I checked the apps, only Google has access to the microphone, the rest only have if the app running (no running app at the background). Not sounds like Bixby, might be google assistant? I will try to disable it and I will see it. This is absolutely random, hard to found out what is it.
It's either an app, running silently in the background (might happen with Google ones) or an assistant (like for disabilities, clock related, etc.) Try a cache cleaning (won't erase any data, passwords, it's safe) and then check the apps again, my guess is one of these Bixby, Google Assistant (check any tasks etc.), the clock with Google or Bixby, Calendar 📅 (check previous tasks, even in Google Calendar, Samsung Calendar app etc.)