You can also take the help of the GainTools OST to PST Converter Tool. This application allows you to bulk convert an OST file to PST format and other file formats. It has a very easy-to-understand & simple GUI, through which any technical and non-technical users can simply handle the software without any help. It converts all OST mailbox emails, contacts, calendars, and other items without the installation of MS Outlook. It is suitable with Windows OS, including Windows 11. You can also use the free trial edition of the software without any cost. Refer: https://www.gaintools.com/ost/pst/