Depends how much, but you’re right.

Lower octane that puts in higher octane aren’t burning the fuel because higher octane needs a hotter spark to burn it all so you’re essentially wasting money or slowly killing your catalytic converter by putting in a higher octane than what your car is meant to use.

On the flip side, lower octane in a car that requires higher means the gas ignites quicker which will cause knocking and can damage the engine.

There’s probably more to it than this, but that is what I was always taught.