I got help from one of the devs of indico.
It turns out that the latest version of indico requires python 3.12.2 at least. Using the default python version lead to an older and unsupported version of indico.
So I added a python_install function to the package for getting an alternate version of python on the server.
He also gave me some recommendations for the install script related to indico deployment.
Now the app installs and works correctly. I am waiting for the Ci tests to finish.
Thanks a lot for your support.