the 2% rule means you don't risk more than 2% of your account on any one trade. if you have $100k, you don't risk more than $2k at a time. it's definitely applicable to crypto. it's a basic risk management strategy that hedges against variance.
even if your trading system is profitable, you could have a run of bad trades. if you trade 20% of your account at a time, you could blow up your account and lose your shirt after only a handful of trades. the 2% rule allows you to survive an unlucky run, and live to trade another day.
How can it work when earning only 2%? how about fees?
It's about position sizing, not take-profit levels. You can take a position worth 2% of your account, then sell at 20% or 200% profit. These are two separate concepts. The 2% rule just limits the amount of capital you can put into a single trade. It doesn't limit how much profit you can make on that trade.
The old guideline still applies: cut your losers early and let your winners run.
Do you mean 2% for stop loss ? With high volatilitas of crypto, i think that too small percentace in crypto trading, for the better use minimum 3% to 5% for stop loss and take profit minimum 10%. Stop loss 2% can be better to use in stocks trading that has lower volatility than crypto.
Stop loss is also a separate (but related) concept.
2% can work. It all depends on the risk vs. reward and your trading style. I trade higher time frames (1-day, 1-week charts) which means I have wide stops, usually wider than 2%.