Hardware/Software: Difference between Protocol and Interface

In terms of software, a protocol refers to a set of standardized rules and procedures that govern how data is transmitted, received, and processed between devices, hardware components or systems.
The protocol specifies the methods for data exchange, including the syntax (format of messages), semantics (meaning of messages), and timing (sequence and synchronization).
The protocol functions include: connection establishment and termination, authentication, data flow control (buffers and data rate transfer), error handling, acknowledgment/feedback, addressing and routing data.

In terms of hardware, an interface refers to the physical and electrical connections that enable communication between devices or hardware components.
The interface defines the size and shape of the connectors, electrical characteristics of the components involved, the materials to be used for connectors manufacturing and assembly or the transfer means.
The interface functions include: physically connect the devices/hardware components, transmitting data to and from devices/hardware components, optionally provide electrical power to devices/hardware componentes.

Protocol can be viewed as a language.
Each language has its own rules (grammar), how to transmit the data (pronunciation, spelling), the data order (syntax) or the data type (letters, words, sentences), among others.
Interface can be viewed as the elements used to transmit that language
The medium could be the air or paper, the air or ink composition for optimal transfer, the shape of the ears and eardrums or eyes and fingers, the vitamins and nutrients they need to function optimally, etc.
So that the same protocol can be used by different interfaces and also the same interface can be used by different protocols.
In production enviroment is key to identify which protocols and interfaces are being used at all times and in all places.
It is important to note that confusion can occur when protocols and interfaces are given similar names or are incorrectly named on a widespread and everyday basis:

Using USB to name both protocol and interface:
Protocol name: USB 3.2 Gen 2x2
Interface name: USB Type-c

Using SDI to name both protocol and interface.
Protocol name: 3G-SDI
Interface name: BNC
In the same way, in production enviroment is key to follow the standards of the protocols and interfaces used. For example by using cheap cables that do not meet the interface requirements could lead to transmission errors or a decrease in the data transfers rates.