I use Blockfi… Voyager and Uphold are easy too. If you’re not concerned with actually holding the BTC on your own drive the cash app is easy hell to buy on.
Also there is an ETF - GBTC. However, it can trade at a massive premium to it’s actual NAV when the supply/demand dynamics pump the ETF price more than the underlying reserves.
A really egregious example of this is BITW which is a top 10 crypto ETF:
Yeah… just a slight premium.
Also the ETFs don’t trade on the weekends but crypto does, so if a black swan event occurs when stonks are closed… everyone else is going to have a huge head start on making you a huge bagholder.