I remember when SFC was first introduced, I excitedly wrote a script to invoke it remotely so I could use it on a user’s pc when they called to fix their problem. To this day I have never run that script. This was in 1998.
I think on mutable distros, or at least arch, you can run a command to reinstall all installed packages, which will verify integrity of the package files (signatures) and then ensure the files in the filesystem match package files? And I think it takes minutes at most, at least for typical setups.
I do think it's also possible to just verify integrity of all files installed from a package, but I don't remember if it required an external utility, pretty sure it's on the arch wiki under pacman/tips and tricks
I've tried using SFC multiple times and had it work zero times. One time after SFC failed to find anything wrong, I ended up fixing the machine by replacing the system file with a copy from a working machine.