Google has updated the Groups interface (what you see) as of November 10, 2020. The new Groups interface will be the default for all ND accounts. There will be no ability to switch back to the Classic Groups interface as that option is no longer available. 

The new design is similar to the other G Suite apps, such as Gmail, and will make Groups more efficient for new and existing customers. Most of the features from Classic Groups are still available in the new interface. New features include:

• Organize your favorite groups with folders
• Create groups quickly with a streamlined creation wizard
• Adjust group settings faster with a consolidated options menu

For a complete list of features missing from Classic Groups in the new Groups interface, view this article from Google. 

Resources for getting started in the new Groups interface:

• How to Create a New Google Group
• New Google Groups Settings Interface
• New Google Groups Quick Reference Guide (pdf)