If you want to convert the OST file without any data loss then you should try the Data Recovery Freeware OST to PST converter . This tool helps to convert the PST file into MBOX, EML, MSG, etc. This tool allows its users to import the OST files to Outlook office 365, Gmail, etc. Moreover, this tool is available for Mac and Windows users.
Try the OST to PST Converter Software, which is the best solution for easily converting all databases from the OST file and also allows you to easily migrate mailbox items from the OST file to multiple file formats such as PST, EML, EMLX, MSG, HTML, and so on. This tool will securely export all emails, contacts, chats, tasks, notes, journals, appointments, and so on from the OST file to PST or other working file formats by following a few simple steps. You can easily try a free demo version of this software, which can convert OST files with up to a few items in each folder to PST for free. Refer:- https://www.softakensoftware.com/ost-to-pst-converter.html