If you are looking for a reliable OST to PST converter I recommend
DataVare OST to PST Converter. It makes it easy to convert inaccessible and orphaned OST files into Outlook PST format without data loss. It is user-friendly and supports all Outlook versions including the latest ones. You can export emails, contacts, calendars, attachments and notes with complete accuracy. It doesn't require Outlook installation. It is a great solution for anyone requiring to recover and migrate OST files efficiently. A free version is also available to try before purchasing.