Though the names sounds similar but the underlying protocols are very much different.
Profibus:
Profibus, short for Process Field Bus, was introduced in the early 1990s and quickly became a widely adopted communication standard in industrial automation. It primarily serves as a fieldbus, connecting field devices such as sensors and actuators to programmable logic controllers (PLCs) and other automation devices.
Each device on a Profibus network must have a unique address, ranging from 1 to 127. This means that up to 127 devices may reside on a single Profibus network.
There are two variations of PROFIBUS in use today; the most commonly used PROFIBUS DP, and the lesser used, application specific, PROFIBUS PA:
PROFIBUS DP (Decentralised Peripherals) is used to operate sensors and actuators via a centralised controller in production automation applications.
PROFIBUS PA (Process Automation) is used to monitor measuring equipment via a process control system in process automation applications.
Profinet
Profinet (Process Field Net) is an open industrial Ethernet communication protocol based on international standards. Profinet was designed for industrial automation applications primarily, to enable communication between various sensors, controllers, devices, machinery and software solutions. Maintained by the Profibus and Profinet International organization, Profinet is one of the most commonly used industrial Ethernet standards thanks to its robust message delivery capabilities and compatibility with other Ethernet-based protocols such as OPC UA
References:
https://www.clarify.io/learn/industrial-protocols