I think the best way is to be taxed when you BUY crypto into fiat AND taxed when you sell crypto back into fiat. This may be unpopular but I think it gets rid of all the problems I mentioned above.
Taxing crypto only when you sell back into fiat has a problem, which is many people don't cash out into fiat. I can just leave it as USD or USDT or any currency on an Exchange, I can even privately sell my bitcoin into cash or goods and services. This negates taxes from BOTH parties which isn't fair to a normal tax payer.
However, taxing crypto while you're buying/selling is dumb considering the volatility of crypto. This just isn't practical nor fair, as it benefits hodlers and fucks with day traders.