Currently, this feature is unavailable for Outlook on the web. The current folder counter represents the unread messages.
As an alternative, to review the folder's total count and storage usage, you can:
- Select the Settings icon | View All Outlook Settings | General | Storage
- Shortcut: Type Storage in the Setting Search bar as shown in the image below. Users sometimes forget that they can search for an Outlook action.
You can provide Microsoft feedback or suggestions directly through the Outlook feedback portal. They have a team that reviews end users' comments. See instructions below.