Share models,libraries,helpers multi applications

Good morning all

I am in the process of migrating all my applications from CI 3 to CI 4.
However, I encounter a small difficulty.
Indeed, on some projects, I have several applications on the same CI instance. I saw that on CI 4 this was also possible. However, I am wondering how to share models, libraries or helpers between these applications.
On CI 3, I put a shared folder at the root containing models / library / helpers and I loaded this folder in the autoload.
Example of structure on CI 3 :
apps
    frontfoffice
        config
        controller
        ...
    backoffice
        config
        controller
        ...

shared
    helpers
    models
    libraries
system
index.php

I can't get the same thing on CI 4. For example, I would like to share the same model between a backoffice and a frontoffice.
Does anyone have any ideas for me to solve this problem?

Thank you in advance

Pierre

Sorry for my english, I'm french