It's probably best to use an inverse BTC ETF. You can also use futures or options.
For a longer position you can short BTC/USDT perpetual futures using a margin account (Binance, FTX...)
For a little more involved position with a more secure counterparty you can short BTC/USD futures on the CME, you'll have to keep the contract expiration in mind though
The CME also offers options on futures contracts but there's barely any volume: https://www.cmegroup.com/trading/equity-index/us-index/bitco...
The simplest approaches would be an inverse ETF or a perpetual short position (only available on crypto exchanges afaik)
