The problem isn't with the use of `screen -x ...` itself, but rather if `ls -l "$(which screen)"` returns something like `-rwsr-xr-x 1 root root ... /usr/bin/screen`, where the `s` in the fourth position indicates the setuid bit is set.
That means the screen binary runs with root privileges.
I use screen almost by default when connecting over SSH, but I've never used -x and didn't know about it.
Habbit from back in the dial-up days when connections got dropped quite frequently. Still relevant with laptop going into sleep mode and such.
So nice to just resume wherever you were as of nothing happened. Or to run jobs in the background, like long compiles, without an additional SSH session.