I have a localhost environment (for debugging purposes) with the 'Manage webhooks' checkbox unchecked. When I create a new multibranch pipeline adding a GitLab project as a source I receive the following error:

Caused by: java.lang.IllegalStateException: Jenkins URL cannot start with http://localhost 
URL is: http://localhost:8080/jenkins/

This happens because after saving, the webhooks are being created for my project. But I've disabled the option to manage webhooks.

As far as I understand, If 'Manage webhooks' option is disabled, then webhooks shouldn't be created.