Hello,
Some brokers does not have BTC/USD, but they have BTC/USDT or BTC/USDC.
My question, is the any difference (in term of day trading profit) between BTC/USD and BTC/USDT?

To sum everything up, here's a simple explanation:
BTC - Crypto
USDT - Crypto
USDC - Crypto
USD- Fiat.
Any of the mentioned currency above can be paired and be exchanged. Brokers (or Exchangers in crypto terminologies), such as Binance, offers both crypto and fiat exchange. And lastly, there are little to no difference at all, USDT and USDC is backed by USD but doesn't mean it really keeps with the price of USD, there can be some time of delays, hence exchanging any pairs would still make the same profit.