Is there's anyway to get fee estimation with vbyte instead of KB using "estimatesmartfee" RPC command? I'm using Bitcoin-core RPC command to get current fee rate, but it returns the fees in KB, I would like to get fee rates in vbyte is that possible?
It is of course already using vbytes; anything else doesn't make sense. Almost everywhere Bitcoin Core reports transaction sizes, they're reported in vbytes (for non-segwit transactions, 1 vbyte = 1 byte, so it was a transparent and compatible update).

However, the unit Bitcoin Core uses is "BTC per 1000 vbyte" rather than the currently more common "satoshi per vbyte".

A Bitcoin Core reported feerate of 0.00123456 BTC/kvb corresponds to 123.456 sat/vbyte.