Meta/Facebook preinstalls an app called Meta Services (previously Facebook services) on a very large percentage of android devices (I’ve never used one without it) and while they claim it helps updates and synchronisation between different meta apps, it is very suspicious. Why preinstall it on devices of people who will potentialy never use a single meta app?
Go to your app list/app management and show system apps and find anything with the words “meta” or “Facebook” then turn off network access for those apps (if you can) and disable them. (eg. Meta app manager, Meta app installer).
https://www.askwoody.com/forums/topic/meta-services-an-android-app-or-not/
https://fixyourandroid.com/about/facebook-app-manager/
https://www.reddit.com/r/GalaxyS20FE/comments/ttmx4t/meta_services/
Edit: Looking around I have found several people complaining that this app is using their ram for 10 hours a day even though they don’t use anything Meta. That’s even more suspicious.
In most apps, there’s several settings you can change to try and fix that. If you ever want to try it again, try using qksms (or another good alternative at the time), and playing with the settings.
I had the exact same issue with signal on my last phone.