MODBUS is the user layer protocol of serial communication, while rs485 and rs232 are the hardware layer protocol of serial communication, these two protocols are completely two different things, in popular terms, the hardware protocol is to describe the transport vehicle, and the user layer protocol says what goods are loaded on the vehicle.
The Modbus communication protocol defines the data interaction mode between the host and the slave in the form of instructions, including the read and write instructions from the host to the slave and the reply format after the read and write instructions are executed by the slave.
Rs485 and rs232 define the hardware structure of data interaction, including what kind of interface chip, communication cable, signal and electrical equality content is used.