They have to find it first, which can be easy or difficult, depending on how motivated you are to make it difficult. You can quite easily make it more difficult than it is for them to walk into a bank and say “freeze this account”.

A US judge ordering a person to turn over their BTC wallet would be check.

Certainly the police seize property citing dubious reasons, but are there examples of judges seizing financial assets without legal authority to do so?

Police can use civil forfeiture to seize property; but can't use civil forfeiture laws to compel you to give up your gmail password. That requires a court order/warrant. Hence the original comment about a judge could compel you into turning over your BTC Wallet.

Whether the reason is valid or not doesn’t matter much to the target of such an order. They still lose access to their funds. People who care about that possibility may want to take steps to make it more difficult for someone to do this to them. That’s all I was saying.

Defying the courts authority is Contempt of Court. If you fail to comply with a judges order, that can lead to incarceration. Continue to defy, can lead to criminal incarceration.