checksum phase in the I2C model shown bellow for si7021
Any standard interface allows you to define how many bytes you wish to receive via I2C using the standard protocol for reading. You can choose yourself how many bytes you want to receive. You either read the two result bytes only, or three bytes if you want the checksum.
The difference is how many bytes to receive so that MCU sends ACK to continue transfer, before the last requested byte is transferred and commanding the MCU to send NAK and stop condition.