It really depends on your country.

But usually capital loss can only be claimed once you sell the bitcoin, at least in my country. You can't claim it in most cases and most countries unless your loss becomes realised. The asset value dropping itself will not mean that you are capable of claiming this as a deduction, because that's still unrealised P/L.

Selling & buying back at the same time could work. But again, you need to consult someone that is professional that will offer you advice based on your own circumstances and the jurisdiction that you are in - not all cases are the same.