In the Copenhagen interpretation, when I look at schrodingers cat, the wavefunction will collapse. After I have looked at it, no way to go back. Information is lost. In many worlds, I just become entangled with the system - and I could theoretically disentangle after. Like quantum computing going to a deterministic outcome in a certain basis.

Showing collapse happened is really tricky because of decoherence. Similar to unmixing coffee and milk. But all systems we have observed so far do not show wave function collapse (granted these systems are generally small, but otherwise decoherence starts messing about).

These are just fundamentally different theories. Not just an interpretation, physically different outcomes.