Finally figured it out. Under the registry key "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Desktop\NameSpace_36354489\DelegateFolders" you're likely to find a key named "{3936E9E4-D92C-4EEE-A85A-BC16D5EA0819}" (default value = "CLSID_FrequentPlacesFolder"). Delete that key and the second list disappears.
I also partially solved the related issue that when you disable "Expand to Current Folder", you cannot expand Home in the navigation pane to show the frequent folders. You can make it expandable (i.e. add the little arrow button), but I can't figure out how to make it expanded by default. To add the arrow, change the value named "Attributes_36354489" from 0x2000000 to 0xA0000000 under the keys "HKEY_CLASSES_ROOT\CLSID{f874310e-b6b7-47dc-bc84-b9e6b38f5903}\ShellFolder" and "HKEY_CLASSES_ROOT\WOW6432Node\CLSID{f874310e-b6b7-47dc-bc84-b9e6b38f5903}\ShellFolder". (That's adding the value of SFGAO_HASSUBFOLDER, described here: https://learn.microsoft.com/en-us/windows/win32/shell/sfgao.)
Hope that helps!