Hello Arnaud,
I was able to create a project in STMCubeIDE for open-amp ping pong application and run successfully on STM32H745i-disco board. Since you have mentioned that this is compatible with RPMSG application on Zephyr, I will use this version for now to interface with Zephyr and will defer upgrade to latest version. Still if you have any information as to what changes are needed to STM code to upgrade to the latest version of open-amp, please let me know. I may be able to work on this and contribute to upstream.
Regards, Murali