I think FiveM should first of all not be responsible for dealing with hackers, GTA 5 itself should take care of that.
Second of all, it’s a bit unethical to add “anti cheat” to a software which in essence is a cheat…
Also you can do plenty of stuff to detect cheaters, Basic sanity checks can be performed to detect teleporters, speedhackers, infinite ammo and even god mode.
And the good 'ol phrase from OWASP:
Keeping critical data on the server side is also a good way to keep hackers at bay.