Webmail:

1) Login to portal.office.com, select outlook

2) Click on the cog wheel 

3) Select Display settings, then click on Focused Inbox tab and select don't sort the message, if you want to enable it click on sort messages into focused and other

In Outlook Desktop app
In the View tab Show focused inbox is disable if it is not highlighted and enabled if it is highlighted

Focused inbox Disabled

Focused inbox Enable