Yeah just create an address that is impossible to generate from a private key. E.g. - bc1iamaburnaddressHgLxD67NK… or something like it.

You could also do a 1 million year timelock or something. But if you don’t have some other lock on it based on a key that you probably don’t have, then there’s no way to really stop the key from being used & no way to verify the key doesn’t exist or was destroyed. The basic and common option is just creating a burn address, which just proves there was no chance the person generated it from a real/known private key, and thus no one can unlock it.