This isn’t trivial on Roblox though nor are you going to get a 0% false positive rate since even in the most popular off-platform games, you’ll still get rubber-banding or outright not be able to move if your connection is really bad. Rollbacks are still ‘detections’ even if we decide not to punish the player for the rollback; it inconveniences the player and could lead to them losing if they get unlucky with the rollback, it is an unfortunate balancing act we need to play as game developers.
This is simply not true, while client anti-cheats are certainly bypassable and shouldn’t be solely relied on; you couldn’t, for example, implement an anti-cheat to prevent free-cam on the server since the camera isn’t replicated to the server. There are many other anti-cheats that are only possible on the client.