Introduction You should always have external SharePoint sites in the Classic Experience. SharePoint offers two different user experiences: Classic and Modern. The Modern experience provides a user interface that is highly adaptive to mobile use, and while some may appreciate the look and feel more than the Classic experience, there are some disadvantages to using the Modern experience when managing site components such as document libraries and lists. Additionally, all external SharePoint sites and site components must be in the Classic experience to ensure that the required legal disclaimer is visible to external stakeholders. By default, Sites and Sub-Sites are implemented using the Classic experience and cannot be changed. However, document libraries, lists and other site components can be changed, either temporarily or permanently. | 
