I can get account balance of each crypto individual through /api/v3/account
but how to get a total of all crypto converted to USD
This needs to be converted on your end, you can calculate the value of the assets in USDT using the ticker price endpoint and then find the rate from USDT to USD or use binance.us api endpoint to know the assets in USD, ex: https://api.binance.us/api/v3/ticker/price?symbol=BTCUSD