Trading with crypto

Sry guys I am pretty new. I have about 20 k in btc ltc ETH and solana

My question is what exactly is meant with trading with cryptos.

I used kraken bitpanda and exodus.

Converting and selling cryptos is pretty expensive. You lose about 2 3 % when you exchange. For example if you convert your btc into tether after it went up and you want to have a stable coin.

So my question ist how is it even worth it or possible to really trade with crypto on crypto wallets when you always pay 3 % fees. Seems like it would be only worth of you stay with it longer and earn 10 % +

Is there a way to pay lower fees?

The only way I be seen is to buy crypto on something like trade Republic where you only buy the value of the key and also don't pay big fees when you sell.

Hope you guys can help me out