Reverting back to the old Bookmarks Manager interface is as simple as it was for reverting back to the old user profiles—using a Chrome Flag. Just go to chrome://flags/#enhanced-bookmarks-experiment, disable the feature, and relaunch Chrome. Alternatively, you can do the following.
- Visit chrome://flags in the URL address box
- Search for “Enable Enhanced Bookmarks”
- Switch “Default” to “Disabled”
- Hit the “Relaunch Now” button