Hi,
If you are interested in a UDP example, you can use the Mongoose Networking Library. It's a lightweight networking library, ideal for embedded devices and it has support for a wide variety of networking protocols, including UDP. The Mongoose API is well documented here.
Moreover, the library contains a wide range of examples for each of its features, for example here you can find some useful UDP examples that can help you.
Since you're looking to use the Ethernet functionality on a CubeIDE application, I have crafted an example of a simple baremetal project running the Mongoose library on the STM32 H755ZI-Q board. It runs on top of Mongoose's own TCP/IP stack, a simpler and lightweight alternative to lwIP.
You can then use the Mongoose examples along with the documentation to easily modify this example as per you required functionalities.
P.S. This project was generated using the Mongoose Wizard tool. The Wizard is a no-code builder that lets you visually design a web UI, but it also generates the entire project (ready to be compiled) for you.
Heads up: I am part of the Mongoose development team and I hope this helps you get started.
