How can I mount a data file (pst) in new outlook. In the classic version this is doable through the File menu which is not available in new outlook.

AVieira_BA, please see if this article helps:

Use Classic Outlook, not New Outlook (slipstick.com)

According to the roadmap, release is scheduled for March 25, 2025:

Outlook: Initial version of PST support in new Outlook for Windows The initial version of PST support in new Outlook for Windows will enable users to open "*.pst" files (a.k.a. Outlook Data Files), read all e-mail messages within the "*.pst" file, and search e-mail messages within the ".pst" file. This initial support is limited to Mail items and is read-only. All Calendar, Contacts, and Tasks data saved in the "*.pst" files are still there, but they cannot be accessed in this initial version. #newoutlookforwindows

Microsoft 365 Roadmap | Microsoft 365

I can see that Outlook users are complaining for several months about this issue. When is expected that Microsoft solve it?

Like other users, I tried to go back to classic version, but is not working (I was compeltly forced to go to the new one!!!).

Hal, I stand corrected about creating new PST files. However, my version of Outlook 365 does not show a "New Items" option as per your screen snag. Instead, I found "More Items >" dropdown by clicking "New Email" dropdown menu.

I completely forgot about creating a PST from Accounts. Thanks for your help.

Now back to the main topic. When will the NEW Outlook support creating and opening PST files?

Klaus, Installing Outlook New does not affect Outlook Classic. If you had it before, it should still be there and be available for use. This article may help:

Use Classic Outlook, not New Outlook (slipstick.com)