If i send BTC to get USDT in ETH Network i pay the ETH Fees and the regular 0,5 - 1% fees but i pay more to fixedfloat, i pay also fees for BTC but why?
Have you ever tried it?
The general swap practice is to take fees (network and services) from the coins you own, which in your case is bitcoin. You'll not be charged any more fees in ETH because you're a USDT (erc20) recipient.
Fixedfloat is a bot but they're centralized, so they may charge higher fees than the network recommends.
I just checked my old safepal wallet, apparently they've been connected to some other exchanges like Bingx and Mexc to use their swap feature without KYC. The service fee is only a flat 0.2%, excluding network fees (out-in).