I would like to suggest the Recoveryfix OST to PST Converter Tool to recover & migrate inaccessible or orphaned OST files. The OST to PST Converter tool quickly converts OST data into PST format while preserving emails, attachments, contacts, calendars, and folder structure. It supports large OST files, ensures data integrity, and offers a simple, user-friendly interface for smooth and secure conversion.

https://www.recoveryfix.com/ost-to-pst-converter.html

To import an OST file into Outlook, converting it to PST format using a reliable tool like GoldyTools OST Converter is the most efficient solution. Trusted and recommended by Microsoft MVPs and IT administrators, this software ensures complete and secure data migration.

GoldyTools supports Outlook 2021, 2019, 2016, and earlier versions, and allows you to convert OST files to multiple formats including PST, EML, HTML, PDF, MSG, and RTF. Whether you're working with large, orphaned, or inaccessible OST files, the tool guarantees full access to all mailbox items—including emails, contacts, calendars, tasks, and notes.
.https://www.goldytools.com/blog/easy-solution-microsoft-ost-to-pst-converter/