Unable to remove "orphaned" Clutter folder from Outlook 365 App (Version 2105)

Did you turn off the Clutter in Outlook on the web?

If so, as I know, the Clutter folder remains in Outlook. It's by design.

Based on my research and test on my Outlook365 client, I found a workaround that MFCMapi tool can be used to hide the Clutter folder. Please refer to the following steps:

1. Download the MFCMapi tool from its official project page (When you use a 64-bit version of Outlook, you’ll need the file starting with MFCMAPI.x64.exe.);

2. Extract the downloaded zip-file and execute mfcmapi.exe;

3. Accept the dialog prompts to get to the main window of MFCMAPI;

4. Choose Session > Logon > select the profile for which you want to change the mailboxs' display names > ok;

5. Double click the mailbox you want to modify in the upper pane;

6. In the Navigation Pane on the left, expand the folder list called “Root - Mailbox” or “Root Container”;

7. Expand the folder list called “Top Information Store”, “IPM_SUBTREE” or “Top of Outlook data file”;

8. Select the Clutter folder, choose: Property-> Advanced-> Edit given property…

7. Type in Property Tag: 0x10F4000B, and then Property Name will display PR_ATTR_HIDDEN;

8. Click OK;

9. In the Property Editor dialog: select Boolean, and click OK;

10. Close all the open MFCMAPI windows.

And then the Clutter folder should now be hidden in Outlook. (Notice: To prevent improper operation from damaging mailbox or data loss, please back up your email data before doing this operation.)

Alright I finally found a solution but it is not completely intuitive. Since Focused Inbox was initially created as an alternative to the Clutter folder, if you temporarily turn on the Focused Inbox Feature (View -> Show Focused Inbox) the Clutter folder immediately disappears. You can then toggle Focused Inbox off again and Clutter will remain gone since the feature has been discontinued.