I can't help but feel like Fall Guys was not the ideal example given just how comically vulnerable it was, it trusted the client for so much instead of running calculations server side you could just tell the server you're at the finish line and disqualify everyone else.
The issue is that because there is no perfect solution even if you have a pretty good all server side solution you’ll still improve by adding client side anti-cheat.
Anti-cheat systems are the compromise that allow games to be played on PCs instead of only locked down dedicated hardware.