If you remove the Facebook app, there are still 3 hidden services that keep telling Facebook all you do on the smartphone.
You need to connect the smartphone with "Developer mode" active and enable Debug so you can connect via adb and list and remove the apps.
You might need to install Andoid SDK that has adb command works on Windows and Linux.
You can remove the spyware malware from Facebook with this commands:
adb shell pm uninstall --user 0 com.facebook.appmanager
adb shell pm uninstall --user 0 com.facebook.katana
adb shell pm uninstall --user 0 com.facebook.services
adb shell pm uninstall --user 0 com.facebook.system
This works on Samsung and Redmi but should work on most smartphones.
You should install some kind of local VPN to block internet access for any app and allow only apps that you need or trust. NoRootFirewall is a great option.
Also install a PiHole so it can resolve ads/spyware/malware before it reaches the net and block all Facebook domains.