Hi @TEST DIALLO
If you have an azure resource like an azure function or web app and you secure that with an app registration, that will create a Service Principal (a way to add your app to azure AD and secure that with AD authentication (very raw explanation))
The service principal for your apps will display under the "Enterprise App" but only under your tenant unless you publish it like this:
https://learn.microsoft.com/en-us/azure/active-directory/manage-apps/v2-howto-app-gallery-listing
if you follow that publish procedure you make it available to other tenants
regarding "My second question, what is the security risk for your company to do not manage these applications "
are you planning to develop an app for other companies to use/integrate with or just for your own company?
App registrations are very safe. Of course there are best practices to secure the Service principal secret or any other authentication means provided: https://learn.microsoft.com/en-us/azure/active-directory/develop/security-best-practices-for-app-registration
Case that information helps, don't forget to vote or mark as Answer to help the community. Cheers!